General tips:
 - Fullscreen gives you better frames and lower input lag at the cost of it being slightly harder to check discord
 - DVa is an "in your face" bully who uses her extremely high burst damage and good mobility + bulk to quickly erase key targets and make space for the rest of her team. Be careful using her at range because more often than not you're wasting her potential
 - Try to get more value out of your abilities, especially defense matrix. You should be using them considerably more often while also taking more care not to waste them in order to get max value out of DVa's kit
 - The time it takes you to switch your focus on to critical targets needs to be cut in half at the absolute least. Think about who is the biggest threat to you and/or your team, and focus them first
Timestamped tips:
[00:47] - You should use your boosters to get to the point. Your team will benefit from being the first to engage, so use movement abilities to get to the point faster
[00:54] - You're shooting from well outside your maximum effective range. DVa likes to be in her opponents' faces
[01:06] - Reaper is behind you! It took you a full four seconds to notice him, which could have caused you serious trouble
[01:13] - Odds are, you won't be able to 1v1 Reaper as DVa. If he's in your face, your best bet is to fly to the rest of your team. Failing that, you should at least use your missiles and defense matrix together to burst down his health
[01:21] - Pick one target and stick to it. By splitting your attention like this, you end up not killing anyone
[01:24] - Standing still against a Junkrat (or in general) is not a smart idea, and it got you killed here. Pay close attention to Orisa's barrier's HP
[01:55] - DVa does a LOT of burst damage, which is her greatest strength. Play to that strength by doing multiple things at the same time. You can shoot while using missiles or defense matrix while using missiles. You can also melee after using your boosters to maximize your burst DPS
[02:16] - Locating Junkrat took way too long here. Pay close attention to audio cues and visual cues (such as his bomb's trajectory) to find him quickly
[02:24] - Excellent use of your boosters! Don't forget about the DVa behind you
[02:35] - Engaging Doomfist was a mistake. At full HP, he manhandles DVa. Generally avoid him unless you're helping your team finish him off or peeling him off squishies
[02:41] - Try to pay more attention to your location in space. Especially when there's a giant pit in the middle of the point...
[02:46] - Good job targeting the Zen, but try to stand slightly closer to get the best use of DVa's shotguns
[02:52] - Once again, it seems you're struggling to find people. Is this an issue with your sensitivity, volume, or awareness? Try to figure out what's causing it and do your best to fix it
[02:56] - Junkrat is very low. Letting him get away is very risky, especially given his burst potential's potency even at low HP. It's best to secure the kill now that you have a chance, even if it would take you slightly out of position
[03:04] - Chasing DVa here is not worth the risk. More so because there's a Junkrat running around somewhere near you
[03:07] - Eating DVa's bullets here doesn't accomplish much. Defense matrix is very valuable ability, so make sure you're only using it if the situation calls for it.
[04:17] - When playing a tank, stay at the front of the team to absorb damage for the squishies behind you. DVa should very seldom be in front of Zenyatta
[04:41] - Your team has the point and a considerable numbers advantage. It's probably worth it to follow Sombra and help her clean up the enemy, though it's not a terrible call to play passively from the point
[04:47] - Reaper has found himself behind you, again. Reaper can absolutely shred teams if he closes in on their backline, so it's your job as a tank to shut him down before he gets too close
[04:50] - Orisa died to Reaper, meaning you're the only tank alive. Right now your focus absolutely must be on the rest of your team, instead of at the choke where the enemy is trickling in
[05:01] - Good kill on the Junkrat. Look at this kill for an example of how to properly use your boosters and missiles aggressively. Do keep in mind that you're now pushes somewhat far up, but you should be okay because Zen is watching you
[05:03] - Sombra is trying to spray you from outside her effective range, and you're trying to spray her from outside yours. Neither of you will accomplish anything. Meanwhile, DVa and Mercy are shredding your HP right next to you! Get back to the point ASAP where you're safe
[05:11] - You lost your mech here because you were trying to fight a 1v4. Disengage sooner to avoid death/demeching
[05:15] - Baby DVa can get away with aggression due to her fairly high DPS and tiny hitbox, but when the enemy has burst heroes like Junkrat and DVa and "pick" heroes like Doomfist, it's best to keep your distance
[06:05] - HUGE play, but sloppy execution. Junkrat and Doomfist both love closed corridors, and had they not been bots you would have been punished hard
[06:06] - Play around healthpacks. There's a mega in the room to your right, which you should pick up so you're not in danger of losing your mech
[06:12] - Charging an enemy while at 19 HP is almost universally a bad idea
[06:28] - It took you 22 seconds to get healing- use your "need healing" voiceline (x by default, iirc) or find a healthpack to stay topped off
[06:32] - Sombra used EMP here, and Orisa used her bongo. You should be as aggressive as possible to capitalize on their ults (not that it matters much at 98% capped)