Finally got around to replace #GnomeMobile with #Phosh on my OnePlus 6T with #postmarketOS. Thanks to @agx and @linuxmobile for the hints. I expected to just add the postmarketos-ui-phosh package but it complained about some conflicts. I had to manually del some postmarketos-ui-gnome-mobile packages and dependencies before I could add phosh.
https://nerdculture.de/@fluchtkapsel/113867941791194707
While doing this I also did a postmarketos-release-upgrade. It's not really end user friendly at the moment but I consider pmOS still in development. After the reboot, I encountered a "Qualcomm Crashdump Mode" message for the first time in my life. A little disturbing, tbh, but after resetting the phone booted into tinydm+phosh as planned.
While GNOME Mobile isn't bad on a small screen, phosh is a little bit more optimized. I could imagine to give GNOME Mobile another try on my Mi Pad 5.