I had this problem today : i just changed UMA buffer size to 4g and the game is now working in game mode
I’m using Xbplay : it work perfect on SteamOS ! You have a trial for 20 minutes for testing (and if you want to remove the trial, you have to pay 5.99$ only one time to have unlimited access)
I tried with Edge method but you still have black bars ( Xbplay no black bars with correct settings )
With Xbplay, u can even add the game from Xbox cloud directly into your Steam library
Don’t play games at 15w and it should be ok
No but you can increase your battery life with undervolt and playing at 30 fps (3h20 playing RDR2)
RDR2 -> 2h30
GTA V -> 3h
Undervolt all to -40 All games locked at 30fps/hz with https://github.com/ryanrudolfoba/SteamDeck-RefreshRateUnlocker
Don’t forget to play with the TDP slider until game is unstable (8w with RDR2 on my Steam Deck) -> low TDP means more battery juice
GTA VI is using the game engine used for GTA V (Rage) so i think OP is right
Default setting + tdp 9w + 30 hz/fps + UMA buffer size to 1go
Why lower limit is 40fps/hz when you can go to 30fps/30hz ?