Wow that 'escalated' quickly Yes I can confirm that UbuntuTouch can be installed on a FP4 Possible with the good documentation/steps and tooling. I installed it with ubports-installer_0.11.2_linux_x86_64_AppImage via my Manjaro NUC box. The installation went smooth! I experienced the unlocking process as a little sweating, because the phone boots several time. And each time you have to go to the intial 'start' screen and enable the USB Debugging again. Now I should spend some time in discovering UT. I've chosen for the 20.04/stable release at first.

Greetings from The Netherlands,
My name is Jan and I like the idea to have fun with a Linux based mobile OS. Certainly with the current developments in the (tech) world. A couple of months ago I started actively to de-google. When I reduced the amount of apps the switch to another android 'taste' would be easier. I bought a Nothing CMF 1 and installed e/os. I host my own nextcloud instance, and this combination works like a charm. I already work with linux boxes for a long time. When I read more about UbuntuTouch and PostmarketOS, I liked the idea to buy an FairPhone4, and do the 'next step'
Cheers, Jan

@Opolork thank you