Coincidentally, I was just trying this before I saw this comment, and I can report that, as of now, there seems to be an issue with the game and supporting BepInEx in general on Linux at least. They stripped all of the Unity DLLs that come with it, and apparently BepInEx on Linux really doesn't like that. I've managed to get BepInEx running on the game by actually downloading the unstripped DLLs and replacing them in the game's Managed folder, however I can't get OFFRestored to load up.
I'll keep trying at it, but for now, forcing the game to Proton Experimental on Linux will make it use the Windows version, which will work with BepInEx. It's so strange, because the Linux version still has Windows bits in it (e.g. DLLs) while some of the core Mono libraries are in the Linux-native .so format. I'm not super experienced with Linux Unity titles, so I'm unsure if this is the norm.
As for Mac, I'll have to dig out my old MacBook and see what I can do! Hopefully it's a bit simpler there since I'd have to figure everything would likely be native to MacOS.