Quick'n'dirty workaround for anyone running into the same problem:
As this issue is correlated with the system font dpi scaling, start PureRef with "QT_SCALE_FACTOR=1.12 PureRef"
Play with the value until it works for you. My system font scale was set to 0.90 so in order to get something above 1.0, QT scaling must at least be 1.1111111.. (quick maths gives 1.0 / 0.9 = 1.1
I'll have to reopen "Ubuntu 20.04 glitches" [1].
This glitchy UI drawing unfortunately still persists in Ubuntu 20.10. with PureRef 1.11.1, contrary to the findings in the other Bug report ([1]). It only appears when the desktop font scaling is changed, for example through Gnome Tweak Tool.
I tested with PureRef 1.11.1 and 1.10.4 on Ubuntu Gnome running on X11 as well as Wayl