Hi Max,
Thanks for the interesting experiment. It builds and runs okay on my Linux (Fedora 33).
There seem to be some changes to the HiDPI functionality, though. On Qt5, I would need to turn on the "High Resolution Icons" to get large enough icons. Now they are too large with the setting on, so I need to turn it off.
The text also becomes pixelated if I drag the window to my second low-DPI screen, which didn't happen before.
On the positive side, the toolbar height is now okay, it was too low on Qt5 (
https://savannah.gnu.org/bugs/?60110). I also no longer experience this bug, although it's still labeled as open:
Best,
Jeroen