I tried with another display, it works!
It seems, for some odd reason, my main display is the cause. Thank you all for help!
P.S.: It's really cool to have this working, so I can now make FP5 my main device. Ubports is such a great project, after leaving Windows to Manjaro, I now can leave the Google ecosystem too and gain back control of my hardware. Just to mention, waydroid works as well very nice. Not everything is perfect (I have issue with bluetooth), but what it offers, is good enough for me, I can live with the workarounds for the rest, until things are fully working sometime in the future (hopefully).