I only ever got Brigand to run on Linux for about 5 minutes with WINE before crashing, and I can't remember the error message. But apparently people are playing it pretty smoothly now on Proton, which makes me happy. The main problem seems to be the sound files.
I hate dealing with audio and video, but I should at least make sure all the sound effects are in the same format. If someone out there has Proton and wants to download this RAR file and replace all the sound files to make sure it works, I'll post a new patch in a day or so with some other updates as well. The new sounds are twice the size, but it's worth it for compatibility.
Download link: https://drive.google.com/file/d/1FPyx1b3N47nwhpgi9LwGjRy3-0CYnPaG/view?usp=sharing