Now that the testing is open for Proton 9, Valve have now updated Proton Experimental to move over to Proton 9 along with a bunch of extra game fixes for Steam Deck / Linux.
I just learned that PROTON_ENABLE_NVAPI=1 to enable DLSS got changed to PROTON_FORCE_NVAPI=1 in Proton 9.0 (including Proton Experimental). Just in case this helps someone in the future.
On another note: Feel free to let me know if you've got a good way to keep up with necessary/useful launch options. I've simply been having a look at what people use on ProtonDB. But I've come to the conclusion that a lot of the posts there use outdated or simply false launch options.
I can't believe how well Helldiver's 2 has worked for me. My friend on Windows has crashed all the time and the anti-cheat is super intrusive. But on Linux, literally no problems. No launch flags or anything, just click play in Steam.
Can you mention what your specs are and whatnot? I've been getting abrupt random crashes over and over from it, and literally exclusively from it from what I can tell.
EDIT: Figured it out. You need to run the game on DirectX 11 instead of 12 for certain cards.
Insert " %command% --use-d3d11 " into the game's launch options in steam. Game runs great now.