Really glad to be usefull!
About the full-screen bug, I've to say that running many Linux builds of Unity3D games between the end of 2015 and 2017 (not less than 100 for sure) I have experienced that one very rarely (unfortunatly I can't remember some games titles now) even using an experimental mesa driver version (a daily build of a development branch) and an integrated graphic card that suports OpenGL version up to 3.3 only. Before that period, sure I remember that when Linux support for Unity3d engine came out, years ago (and the Engine Editor Linux version wasn't released yet), games where often full of graphic drivers related bugs like that one (expecially with Mesa and Ati-Catalyst drivers). So maybe it's something related with your Unity3D Engine version, as you have said. However I can't exclude that on Unity3D forum there is some work-around that avoids you from change the Engine version.
Anyway as always thanks for your attention and your work!