I followed this guide: https://forums.ubports.com/topic/4964/fairphone-3-fp3
downloaded stable GITLAB CI

I flashed boot.img and system.img, also used TWRP, stuck at android bootloader start screen
flashed boot.img and system.img again, stuck at start again

I also tried an older one but - nothing
Now I need a step-by-step guide from YOU and much help

thank you for help!!!

The Problem was that twrp broke the data partition and the recovery repaired it so when ubuntu-touch doesn't boot, you have to try this.