Ok, second time is the charm
I switched USB cable (it was probably bad), ordered wiping user data and used 24.04-stable for flashing...

Flashing worked the second time and now I'm on UT on my FP5

It is quote save, but not sure, if I recommended it in it's current state:

• the GUI has lags during starting of apps and between switching apps
• the power/thumb reader button is "always on", so any touch activates it.
  Also, the phone reboots from time to time (not frequently - once in a week or so).

Otherwise, the phone is pretty ok to use with 22.04 20.04.

Hello fellow Ubuntistas,
I'm thinking about migrating myself to a "proper" UT device for a change,,,,,

...and I have some questions reg. FP5:

• Does it need to be unlocked in any way?
• What Android is required to be flashed in order to work properly with UT ?
  • Are there any specific Android images? Where to get those?
• Can this device be re-flashed between Adnroid and UT without a hassle? (I plan to use the device for both OSes kindof interchangeably...)
• Are there any caveats for using UT on FP5 as a daily driver? (I saw bad photo quality on some devices, hanging camera/ media recording/media playback, troubles with WiFi hotspots not working, ring tones disappearing after a period of time without reboots, etc etc...)

Thanks a lot for your comments