Update: I just uploaded another beta for Linux only. It overrides the previous download, but you will need to download it again.
If all is well, this should fix the incorrect D-pad mapping on Linux for Xbox controllers.
Unfortunately I don't have any working Xbox controllers to test it on here, so please let me know how it goes!
Edit: I dug out an old Xbox 360 controller which I thought was broken but has magically started working for me. I think it should use the same mappings. Everything is working fine EXCEPT that up/down on both the analogue stick and the D-pad are inverted. Horizontal is fine. 🥴