After a very rocky start, It's finally working fully in game mode, and yes, multiplayer's working too!
I jumped into an SOS call with three other players, and we were in the game with zero hassles. I did got booted from a couple of lobbies (maybe connection issues or just random kicks), but overall, it's smooth sailing now.
I can run the game now without any Proton compatibility, and it worked! There have been a couple of hotfixes on the Proton side and a couple of patches on HELLDIVERS 2 side, which all in all is pretty impressive in just a day.
Heads up for first-timers: you might hit a black screen for a bit at the start, first run can take 5 to 10 minutes to get going but after that its around 1 minute.
Settings-wise, start with the low preset and keep the render scale on Ultra for the best look.
Steer clear of full-screen in other modes to dodge glitches, but in game mode, you shouldn't have an issue.
My go-to setup is VSync off, camera shake on weak (for a bit of a rumble!), and graphics with depth of field off on the low preset. I also tweaked texture quality to medium, render distance to high, and terrain quality to medium, plus medium settings for vegetation and rubble density. Oh, and don't forget to turn on anti-aliasing. With all this, you're looking at a steady 30 FPS, even when things get wild on screen.
Missions are quick and easy, but there's lots to explore, especially if you find it a tad easy. So now that "HELLDIVERS 2" is all set on Steam Deck with multiplayer, why not jump back in?
I'll leave you with some gameplay footage – just the game, no chatter – so you can get a feel for how it plays and performs. Catch you next time, and happy gaming!