I've verified the game files and I've tried several different version of wine, including 5.19, 5.18, proton-5.0-9 (steams), 4.11, and 5.9. I deleted the compatdata pfx between tries.
I've also tried deleting the libmpg123.dll file and doing touch libmpg123.dll, but that also fails.
Seems like proton-5.13 runs the game :-) I've only played 4-5 levels thus far, but no issues at all - sound, music, animations, UI, everything is working perfectly.
I'm not sure what to do, so I'll just leave this ticket open.
Nice timing with 5.13!
Compatibility Report
System Information
I confirm:
steam-1367550.log
Symptoms
Game doesn't start. It's probably related to this line in the log
5726.025:00d0:00d4:err:module:import_dll Loading library libmpg123.dll (which is needed by L"Z:\\media\\folk\\Zoom\\Steam\\steamapps\\common\\Kingdom Rush Vengeance\\Kingdom Rush Vengeance.exe") failed (error c0000020).Reproduction