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).

@Fuseteam tested on my FP4. The switch beetween headphones and speaker is automatic, music playing works well but when I have a call it switches back to phone speaker. I have to re-enter this commandline after reboot : pacmd load-module module-udev-detect

What happens to the device screen? It should display a virtual touchpad. If it does that and your external display at least detects it then that should mean it is compatible. There's a bug right now that wired external display only works once. After the initial connection, it'll just display black. You'll need to reboot to make it work again.