instructions

Found out how to enable DLCs in 1.2.1.

Edit the file Crusader.Kings.III.v1.2.1\binaries\SteamConfig.ini

(make sure it's this SteamConfig.ini as there are several)

Look for the section like:

;UnLockListedDLCOnly=1
[DLC]
;SET DLC USE "APPID=NAME"

And replace it with:

UnLockListedDLCOnly=1
[DLC]
;SET DLC USE "APPID=NAME"
203770 = Crusader Kings II
203772 = Crusader Kings II: Dynasty CoA Pack 1
203773 = Crusader Kings II: Mongol Graphics Pack
203774 = Crusader Kings II: Songs of Albion
203775 = Crusader Kings II: Songs of Faith
203776 = Crusader Kings II: Ruler Designer
203777 = Crusader Kings II: Songs of the Holy Land
203778 = Crusader Kings II: Sword of Islam
210892 = Crusader Kings II: African Unit Pack
210893 = Crusader Kings II: Songs of the Caliph
210894 = Crusader Kings II: Dynasty Shields II
210895 = Crusader Kings II: Legacy of Rome
210896 = Crusader Kings II: Byzantine Unit Pack
210897 = Crusader Kings II: African Portraits
210898 = Crusader Kings II: Mediterranean Portraits
210899 = Crusader Kings II: Russian Unit Pack
210900 = Crusader Kings II: Russian Portraits
210901 = Crusader Kings II: Songs of Byzantium
210902 = Crusader Kings II: Sunset Invasion
210903 = Crusader Kings II: Songs of the Rus
210904 = Crusader Kings II: Norse Portraits
210905 = Crusader Kings II: Norse Unit Pack
210906 = Crusader Kings II: The Republic
210907 = Crusader Kings II: Songs of Prosperity
210908 = Crusader Kings II: The Old Gods
226660 = Crusader Kings II: Hymns to the Old Gods
226662 = Crusader Kings II: Celtic Unit Pack
226663 = Crusader Kings II: Celtic Portraits
226664 = Crusader Kings II: Dynasty Shield III
226665 = Crusader Kings II: Europa Universalis IV Converter
226666 = Crusader Kings II Customization Pack DLC
226667 = Crusader Kings II: Sons of Abraham
226668 = Crusader Kings II: Military Orders Unit Pack
226669 = Crusader Kings II: Warriors of Faith Unit Pack
226670 = Crusader Kings II: Hymns of Abraham
226671 = Crusader Kings II: Songs of Yuletide
226672 = Crusader Kings II: Saxon Unit Pack
226673 = Crusader Kings II: Finno-Ugric Unit Pack
279600 = Crusader Kings II: Rajas of India
279601 = Crusader Kings II: Turkish Unit Pack
279602 = Crusader Kings II: Turkish Portraits
279603 = Crusader Kings II: Songs of India
292980 = Crusader Kings II: Persian Unit Pack
292981 = Crusader Kings II: Persian Portraits
292982 = Crusader Kings II: Charlemagne
292983 = Crusader Kings II: Early Western Clothing Pack
292984 = Crusader Kings II: Early Eastern Clothing Pack
292985 = Crusader Kings II: Dynasty Shields Charlemagne
326530 = Crusader Kings II: The Song of Roland Ebook
329010 = Crusader Kings II: Way of Life
329011 = Crusader Kings II: Iberian Unit Pack
329012 = Crusader Kings II: Iberian Portraits
329013 = Crusader Kings II: Tales of Treachery EBook
354330 = Crusader Kings II: Horse Lords
354331 = Crusader Kings II: Horse Lords Content Pack
373940 = Crusader Kings II: Orchestral House Lords
394320 = Crusader Kings II: Conclave
394321 = Crusader Kings II: Conclave Content Pack
401660 = Crusader Kings II: Viking Metal
428720 = Crusader Kings II: South Indian Portraits
449980 = Crusader Kings II: The Reaper's Due
449981 = Crusader Kings II: The Reaper's Due Content Pack
472070 = Crusader Kings II: Full Plate Metal
530780 = Crusader Kings II: Monks and Mystics
592800 = Crusader Kings II: South Indian Portraits 5 Year Anniversary Gift
601270 = Crusader Kings II: Hymns of Revelation
616160 = Crusader Kings II: Ultimate Music Pack Collection
616170 = Crusader Kings II: Ultimate Portrait Pack Collection
616180 = Crusader Kings II: Ultimate Unit Pack Collection
616210 = Crusader Kings II: Dynasty Shield Pack
640140 = Crusader Kings II: Jade Dragon
756660 = Crusader Kings II: Holy Fury
949870 = Crusader Kings II: Pagan Fury
1167860 = Crusader Kings II: Pagan Fury - Warrior Queen
1296730 = Crusader Kings III: Garments of the Holy Roman Empire
1296731 = Crusader Kings III: Fashion of the Abbasid Court