Hmm.

Both games you listed appear to run in Proton.

Dave the Diver is a Unity game, and Doom (2016) uses id Tech 6, so not a lot of common underlying technical infrastructure at the game level. I can't imagine that it's a common bug in both games.

That does kind of suggest something related to Proton, between Linux and the game, but I don't know of anything that could create a backlog at the Proton level. I mean, keyboard events aren't terribly heavyweight.

I haven't played Doom (2016), but it's a multiplayer game and some multiplayer games might have network latency for movement produce delay, but not for simply panning the camera

though I'd think that this would have more-sophisticated client-side prediction stuff; Quake II did. Dave the Diver is singleplayer, though, so if the mechanism is the same, shouldn't be a network issue.

I don't know, frankly. Kind of drawing a blank. Maybe try, in Steam's Compatibility settings for the game, a different version of Proton? Not that I can think of a specific mechanism that would cause this, but I can't think of much else that would be shared between the games, wouldn't affect the mouse, and would affect the keyboard, and that you could readily change.

EDIT: One other possibility

maybe try disabling Steam Input for the game and see if it affects the issue? Steam does do some processing. I can't think of any reason that it'd insert a lot of latency, but it'd be one of the few other things that would live between the kernel and the game.

EDIT2: Actually, no...I don't think that Steam Input touches keyboard input, based on a quick search. Just controller stuff.

EDIT3: Oh, wait. Gamescope. I've never intentionally used it, but it's some kind of mini-compositor that Steam uses.

And it looks like it touches keyboard input:

https://github.com/ValveSoftware/gamescope/issues/1460

I don't know much about Bazzite, but I understand that it's a Fedora distro aimed at being an alternative to SteamOS, so I could believe that they use gamescope.

kagis

https://universal-blue.discourse.group/t/gamescope-gamemode-for-desktop/3893

With bazzite there is no need to install gamescope as it is baked onto the image

It looks, from that page, like there's some global toggle for gamescope, and people normally enable it on a per-game basis by adding it to the game's launch properties in Steam, but I can't give a lot of advice there; haven't used it myself.

I might try disabling gamescope, if you're using it, and see if the issue vanishes.

And...hmm...on that note, maybe also try disabling the Steam Overlay. That touches keyboard input, and also touches the video display.

https://help.steampowered.com/en/faqs/view/3978-072C-18DF-FBF9

Open the Steam client and navigate to the Steam > Settings > In-game tab. Toggle on Enable the Steam Overlay while in-game.

Just to see if that makes the issue go away.