I would add that there is some kind of major performance regression on the cpu side in 5.4 compared to 5.3, which is highlighted by the deck’s meager hardware. My game gets ~80fps on medium scalability in 5.3.2 on the steam deck, but only mid 30’s when built with 5.4.4. Switching to low scalability doesn’t improve things, so it appears unrelated to gpu.
I did a little comparing and stat game shows tick time a little bit worse on the deck (2-3ms). There’s gotta be other stuff to blame too, but I don’t really have time to chase it down. Just gonna stick with 5.3, and maybe stay there forever 
For anyone stumbling on this thread, I would say avoid 5.4.