This is unfortunately a common issue with games that use the MonoGame library (not actually XNA nor Wine Mono's FNA replacement but another implementation of the XNA API shipped by the game itself). For WMA files that have not yet been transcoded, Proton sends a generic video/audio stream to the application. As I understand it, it's not even possible to parse the file enough to determine that it's only audio, so Proton always sends video to the application. MonoGame rejects it for having a video stream.
And since MonoGame ships with the game, we can't change this behavior.
The only solution on Proton's end is to wait for the media to be transcoded on Valve's servers. But since this game defaults to native, that's unlikely to happen.
Game developers can fix this by providing the media in an unencumbered format.
After writing that, it occurred to me that we could work around it in Proton by having a separate mode that disables the video stream, so I pushed that to bleeding-edge experimental: https://github.com/ValveSoftware/Proton/commit/cf5de03a49454c04f225dbefabbedc38a9828f87 https://github.com/ValveSoftware/Proton/commit/bea1fa891a3402b0a8f29e74e1077da524d7cbfe
You'll likely be missing some audio, though.
@madewokherd just tried bleeding-edge and it fixed... there are just two intro logos that, to be honest, I don't recall having sound anyway in the native version... thank you
Compatibility Report
System Information
I confirm:
Proton Experimental logs: steam-283640.tar.gz
Symptoms
Reproduction