Well, we're making progress. The Linux version now displays the GUI correctly. The bad news is that its login appears to stall exactly the same way that the Mac app does. This is what I see after authorizing a login (confirmed both with Firefox and Chrome as the Itch intermediary):
Since macOS uses a modified BSD under the hood, I'm not surprised that the behaviour between Linux and macOS is similar.
I don't really know anything about Javascript, so I'm unsure at this point what I can do. That said, given the parity of apparent behaviour on Linux, you might consider installing VirtualBox and Linux for doing eyes-on troubleshooting. Both are free.