Worked like a charm on Ubuntu 20.04, using Proton 7.0.3 as its compatibility tool which I had to set explicitly. To do that, open your library, navigate to SWTOR (after downloading), right-click -> Properties -> Compatibility -> Check "Force the use of a specific compatibility tool" -> Select a version of Proton that looks right to you (7.0.3 worked at the time of writing). I didn't have any bit raider issues (not sure that's a thing anymore?) and didn't follow the corresponding steps mentioned above, just a regular installation.