Answers

Please know it might be not full list.

2018.08.07
https://twitter.com/yozoramel/status/1027125562941177856
First collaboration of first generation.
2018.09.11
https://twitter.com/akirosenthal/status/1039413724329566208
Collaboration with Aki.
2018.09.15
https://twitter.com/yozoramel/status/1040871193870512128
Collaboration with Matsuri.
2018.09.17
https://twitter.com/yozoramel/status/1041480402815246337
Collaboration with Aki and Haachama.
2018.09.18
https://twitter.com/yozoramel/status/1041824821171183616
Collaboration with Choco.
2018.09.23
https://twitter.com/yozoramel/status/1043133502625968133
Collaboration with Aki.
2018.09.24
https://twitter.com/yozoramel/status/1044257453825650688
Collaboration with Choco.
2018.10.10
https://twitter.com/yozoramel/status/1050016296400707584
Collaboration with Hero, Choco, Roboco and Aqua.
2018.10.21
https://twitter.com/yozoramel/status/1053990114483818502
Collaboration with Choco.
2018.10.22
https://twitter.com/yozoramel/status/1054286656398749696
Blonde collaboration.
2018.10.24
https://twitter.com/yozoramel/status/1055067131295854592
Collaboration with Hero.
2018.11.04
https://twitter.com/yozoramel/status/1059054317334712320
Collaboration with Subaru.
2018.11.09
https://twitter.com/yozoramel/status/1060841160434798592
Blonde collaboration.
2018.12.11
https://twitter.com/yozoramel/status/1072417659935956993
Collaboration with Roboco.
2019.01.08
https://twitter.com/yozoramel/status/1082555072142180352
Collaboration with Fubuki.
2019.01.12
https://twitter.com/ryugu_ura/status/1083851583509544962
Collaboration with Ura.
2019.01.13
https://twitter.com/Haneru_Inaba/status/1084468737221120001
Big collaboration.
2019.02.05
https://twitter.com/yozoramel/status/1092785410390937601
Collaboration with Patra.
2019.02.06
https://twitter.com/yozoramel/status/1092973575059910656
Collaboration with Choco.
2019.02.09
https://twitter.com/akaihaato/status/1094179015651250176
Collaboration with Haachama.
2019.02.10
https://twitter.com/akirosenthal/status/1094632338795855877
Collaboration with Aki and Matsuri.
2019.02.11
https://twitter.com/yozoramel/status/1094886907396349952
Collaboration with Choco and Megu.
2019.03.02
https://twitter.com/yozoramel/status/1101692157587406849
Could not find collaboration.
2019.04.23
https://twitter.com/yuzukichococh/status/1120701991678689281
Big collaboration.
2019.04.29
https://twitter.com/yozoramel/status/1122909936067809280
Collaboration with Hinako, Tamaki and Choco.
2019.05.13
https://twitter.com/yozoramel/status/1127820308507848704
Collaboration with Matsuri.
2019.05.20
https://twitter.com/yozoramel/status/1130230301521616901
Collaboration with Shion, Roboco, Matsuri and Choco.
2019.05.21
https://twitter.com/yozoramel/status/1130800968872804353
Collaboration with Onomachi.
2019.05.24
https://twitter.com/yozoramel/status/1131893259079307265
Big collaboration.
2019.05.28
https://twitter.com/yozoramel/status/1133400231255527424
Collaboration with Korone.
2019.05.31
https://twitter.com/yozoramel/status/1134431558826319872
Big collaboration.
2019.06.02
https://twitter.com/yozoramel/status/1135140645767487488
Collaboration with first generation.
2019.06.07
https://twitter.com/yozoramel/status/1136954881422397440
Collaboration with Era.
2019.06.16
https://twitter.com/warabeda_meiji/status/1140180312720211969
Collaboration with Meiji.
2019.06.30
https://twitter.com/yozoramel/status/1145342744740524033
Very very big collaboration.
2019.07.03
https://twitter.com/yozoramel/status/1146374841269805057
Collaboration with Suisei.
2019.07.05
https://twitter.com/yozoramel/status/1146723228607340544
Collaboration with Okayu.
2019.07.11
https://twitter.com/yozoramel/status/1149327879827673088
Collaboration with Onomachi.
2019.07.12
https://twitter.com/yozoramel/status/1149687369173311488
Big collaboration.
2019.07.16
https://twitter.com/yozoramel/status/1151063516918550528
Collaboration with Choco.
2019.09.11
https://twitter.com/yozoramel/status/1171745567350767616
Collaboration with Marine.
2019.09.16
https://twitter.com/yozoramel/status/1173445124933615617
Collaboration with Flare.
2019.09.17
https://twitter.com/yozoramel/status/1173737011359830016
Collaboration with Noel.
2019.09.19
https://twitter.com/yozoramel/status/1174662014917996544
Collaboration with Rushia.
2019.09.24
https://twitter.com/yozoramel/status/1176408656415350784
Collaboration with Haachama.
2019.09.26
https://twitter.com/yozoramel/status/1177559257836744705
Collaboration with Pekora.
2019.10.02
https://twitter.com/yozoramel/status/1179364936738377728
Big collaboration.
2019.10.07
https://twitter.com/yozoramel/status/1181231487850409986
Collaboration with AZKi.
2019.11.06
https://twitter.com/yozoramel/status/1191848971217469441
Could not find collaboration.
2019.11.12
https://twitter.com/yozoramel/status/1194223603694178304
Collaboration with Marine.
2019.11.21
https://twitter.com/yozoramel/status/1197444503960817665
Big collaboration.
2019.11.23
https://twitter.com/yozoramel/status/1198233151174131714
Collaboration with Subaru.
2019.11.29
https://twitter.com/yozoramel/status/1200357463792353280
Collaboration with Haneru.
2019.12.21
https://twitter.com/yuzukichococh/status/1208014438340513793
Big collaboration.
2020.01.19
https://twitter.com/yozoramel/status/1218741353384800256
Collaboration with Noel.
2020.04.26
https://twitter.com/yozoramel/status/1254408820672978944
Collaboration with Mishiro.
2020.05.04
https://twitter.com/yozoramel/status/1257271161504673792
Collaboration with Izumi.
2020.06.28
https://twitter.com/yozoramel/status/1277239572351442944
Collaboration with Kanata.
2020.06.30
https://twitter.com/yozoramel/status/1277912100724068353
Collaboration with Towa.
2020.06.30
https://twitter.com/yozoramel/status/1277955463854739458
Collaboration with Izumi.
2020.07.02
https://www.youtube.com/watch?v=ybUCpY_h9K8
Collaboration with Kanata.
2020.07.05
https://www.youtube.com/watch?v=FzMDdA-mhOk
Collaboration with Watame, Flare and Choco.
2020.07.06
https://twitter.com/yozoramel/status/1280079290466332673
Collaboration with Watame.
2020.07.06
Cannot find tweet but there was collaboration with Roboco and Izumi.
https://www.youtube.com/watch?v=Bhi00DgsOVY
2020.07.08
https://www.youtube.com/watch?v=eZoTBLmrlz4
Collaboration with Kanata.
2020.07.09
https://twitter.com/yozoramel/status/1281252912237178883
Collaboration with Choco.
2020.07.10
https://twitter.com/yozoramel/status/1281573970202947584
Collaboration with Matsuri.
2020.07.12
https://twitter.com/yozoramel/status/1282231212250030080
Collaboration with Luna.
2020.07.15
https://twitter.com/yozoramel/status/1283273150210293760
Collaboration with Choco.
2020.07.27
https://www.youtube.com/watch?v=vH3ymT6sIJ4
Collaboration with Aki.
2020.07.29
https://www.youtube.com/watch?v=yi_y9xLolSU
Big collaboration.
2020.07.30
https://www.youtube.com/watch?v=VmRD5sBzCCg
Collaboration with Watame.
2020.08.13
https://www.youtube.com/watch?v=WVQ11nZUVRw
Collaboration with Towa.
2020.08.14
https://www.youtube.com/watch?v=2eNzcvW6WQY
Collaboration with Watame, Flare and Choco.
2020.08.22
https://www.youtube.com/watch?v=L7fdt8NZCCQ
Collaboration with Choco.
2020.08.26
https://twitter.com/yozoramel/status/1298654078994542592
Collaboration with Luna and Noel.
2020.09.29
https://www.youtube.com/watch?v=sxRRqlioqM4
https://www.youtube.com/watch?v=VpYLtASXaSI
Collaboration with Izumi, Achika and Anko.
2020.10.09
https://www.youtube.com/watch?v=iVgwEia_4zY
Collaboration with Choco.
2020.10.13
https://www.youtube.com/watch?v=3qPuwYhCUPY
Collaboration with Izumi, Achika and Anko.
2020.11.15
https://www.youtube.com/watch?v=XK1BKrA2pug
Collaboration with Kanata, Polka, Mio and Rushia.
2020.11.25
https://www.youtube.com/watch?v=hNM2LE7tQQk
Collaboration with Izumi.
2020.12.10
https://www.youtube.com/watch?v=P3CxKm0IhpA
Collaboration with Rube.
2020.12.19
https://youtube.com/watch?v=iFRN48wMV64 (Mel)
https://youtube.com/watch?v=t5LgtAt66to (Suisei)
Collaboration with Suisei.
2020.12.21
https://youtube.com/watch?v=q-ead3i6oZU
Collaboration with Choco.
2020.12.26
https://youtube.com/watch?v=-2G39G_D5Cg
Collaboration with Aki and Choco.
2021.01.12
https://www.youtube.com/watch?v=PVlIP732UBM
Collaboration with Choco, Aki and Watame.
2021.01.16
https://www.youtube.com/watch?v=JEmUxqYztAM
Collaboration with Flare, Aki, Roboco and Aqua.
2021.01.19
https://www.youtube.com/watch?v=ucLwtAAp__o
Collaboration with Ollie.
2021.01.28
https://www.youtube.com/watch?v=EWl0t1G-RBs
Collaboration with Amelia.
2021.02.04
https://www.youtube.com/watch?v=blqykZwvInY
Nijisanji and hololive Among Us collaboration.
2021.02.13
https://www.youtube.com/watch?v=uoc8WfsUYh8
Collaboration with Lamy, Choco, Ayame and Matsuri.
2021.02.24
https://www.youtube.com/watch?v=psEh21WvXN8
Among Us collaboration.
2021.02.26
https://www.youtube.com/watch?v=oqUFc0ITMs0
Collaboration with Reine.
https://twitter.com/hololivetv/status/1365281243248533512
Subaru, Watame and Nene collaboration.
2021.02.27
https://www.youtube.com/watch?v=-WTep9tOv60
Collaboration with Ina.
2021.03.02
https://www.youtube.com/watch?v=G6d5E3-WZp0
Among Us collaboration.

Answers.
1. Why Mel in hololive !?!?!?!?! Only for money and barely streams !!!!!!!
Please do not think that if you do not care about hololive Mel does same. About streaming: As you see Mel did a lot of collaborations (according to list 96 but please know it might be not full !) and it number fell around stalking incident. Mel did not do a lot stream since summer because she was a lot of busy, then busy because moving and then holoFES lessons and sadly after Bloom was sick. But said in March wants to stream a lot !!!（＾∇＾）

2. Mel hates collaborations and never talks on them !!!!!!!!
Mel is a shy and introverted person and admits herself that she is not very good at collaborations.
https://twitter.com/yozoramel/status/1163325723228008448

3. What happen to Mel !?!?!?!? No stream for 300 weeks !!!!!!!!!!
Please check Twitter because I am sure if you really cared it would be first check you do.

4. Mel graduate soon !!!!!!!!!!!!!!!!!!!!!!!!!!!
No. If you watched birthday stream or at least seen clip of Mel's letter from here then you know that Mel wanted to graduate but Kapumin gave Mel a lot of support and love so she continued fighting and never gave up.

5. About Mel stalking explaining here 23833567 or https://twitter.com/zeroblade/status/1261713122944942080 (They are different.)

6. Mel leech !!! Nobody cares Mel that is why a lot holoEN collaborations !!
Mel is doing a lot collaborations and not only with foreign hololive. If you actually believe written above then please read in dictionary meaning of word "friendship". Also Mel is actively studying English and holoEN can help !

I hope that answered everything new people have about Mel. May add more later.