No, the audio backend on Linux running through Wine
needs Windows Media Foundation, there are no ifs/ands/buts about that, not going to argue with the
API behind me on that. I don't use Lutris, so I'm wondering if your problem is somehow in there. Windows always had the minimal amount of libraries for WMF to work since Vista, so of course it'll have sound (talking about Windows, not Wine). WMF will not affect performance (though the whole Qt4 vs Qt5 that the binaries were compiled on may be the difference, Qt5 definitely *needs* WMF, I can't recall what Qt4 used), the API either works or doesn't, so something else has happened in your setup. SteamDeck does support screenshots in Gamescope. Hold the Steam button long enough for the 'controls' to pop up. Steam+R1.
Edit: The mf-install I used came from
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(no longer exists), but it's the same as what you have.
I'll probably have some time later today to figure out how to get it running on SteamDeck, yesterday I was far too busy. Will post back.
Edit: The Linux version uploaded to this thread is Qt5 and it expects Qt5 libraries. I don't have my original Linux source to build it for Qt6 native. I'm not sure if the SteamDeck even has all of the libraries needed, some distros only install certain ones. I'll look at the Windows version for now.
Edit: No performance issue seen on my SteamDeck with either version. 18.5% average CPU, GPU usage is nearly non-existent.
Edit: After installing WMF on my SteamDeck, the *Qt* backend spams 'play' but the WMF mf-install is incomplete (need the cab version, I think), so it doesn't like the WAV output and won't play, but Qt keeps expecting it to play. Does result in a elevation of CPU usage but not like what you reported. (I wrote a simple shell script that gets executed as a 'Linux' game for steam and it automatically sets up the mf-install and then runs a version of Proton that should exist on all SteamDecks for the game. That part is working (auto-mf-install, launch game), but the mf-install isn't the cab version. Trying to find the cab version, got a lot going on.
Edit: Now dealing with x86 vs x64 issues.
Edit: Making progress, taking forever to download an archived version of KB976932 to use.
Edit: Roadblock with Proton's stdin/out redirection. Wondering how to get around copyright issues of distributing files manually extracted from cab. (Side note, Jack-o-nine-tails version cannot ever be ported to Qt6 without a ground-up rewrite because of entire API changes to WebKit (gone, WebEngine is the new and it's radically different). So there will never be a native Linux version for Qt6/SteamDeck unless it's rewritten.
Edit: Got it working, but the audio crackling and phasing is entirely impossible. I'm just going to take a peek at how much work it'd be to try to rewrite the UI and bridge using same Qsp lib and Onigurama (static compile, copy over kind of thing).
Edit: If you still want to try running with Qt5, you can remount SteamDeck as read/write and sudo pacman -S ...the various packages (they use different names on Arch-based distros) to get it working natively. You can always restore the SteamDeck using a raw-write, but...this is NOT recommended for newcomers at *ALL*, you might not be capable of restoring it. I'd probably say setup a version of Windows on a thumb drive that's capable of handling the read/write speeds and boot from that, then run Jack-o-nine-tails.
Edit: Eh, this would take too long to rewrite *while keeping compatibility*. Stream Play it (should be easy) or run Windows via a nano/pico drive or something, for now.