I was able to play Brawlhalla fine until a few weeks ago, but with the new update coming to Protona and Endeavouros, I started having a lot of lag problems and now I cannot open the game. All Endeavours OS Brawlhalla players, I am waiting for your help. For possible updates, my discord account is uh3912.
Have you already tried the older Proton versions?
PS: Welcome to the most comfortable Arch community! Hope you learn and a lot and enjoy your time here. 
As @anon93652015 stated, try an older version of Proton. I find that version 7 is very stable with Windows games; been running Path of Exile for 2-3 weeks flawlessly after switching to 7 due to various glitches.
Interestingly enough, these posters on the ProtonDB site are almost all using version 8: https://www.protondb.com/app/291550
Yes, the 7.6th version of Proton used to work, but it is not working now, you need to find the correct startup options codes…