Do you have the latest patch from the download folder applied to the Linux version? Another user had the same black screen issue and applying the patch fixed it. And for the Windows version through proton, what happens when it fails to run? The same black screen, or is there an error?
Viewing post in Crossdressing in Camelot comments
Hm, it's odd that patch didn't fix things. It could be a permissions issue, since the patch itself wasn't uploaded as a .tar file, maybe? You could try applying this patch instead to see if that fixes it: https://mega.nz/file/YbgTwbia#NeqkZGj4qLah2Nuc8Hw21PJvRc9_OvvhWZHUjALttjI
Or if you know how to do so, you could ensure the game has execute permissions. I don't recall how to do that on Linux off the top of my head.
If those don't work, have you played a previous version of the game? Trying to determine if the issue is specific to the latest version. If you haven't you could try testing the most recent version before this one: https://mega.nz/file/oeJRFBSb#3hyHRr3LdZCXhk8l31RCZIhD-3ox4dgFDiOOLYdFtIc
Other than that the only thing I can think to mention is to try moving the game to your desktop and then running from there. Sometimes issues arise with long filepaths, so that could fix it. (And if it does fix things you just need to put it somewhere with a shorter filepath, not necessarily on your desktop.)
If none of that works let me know. I don't know what else to try at the moment but maybe something will come up.