@mihai said in reflash after installing Ubuntu Touch:

UBports installer(0.10.0) (I, ve updated it, first I, ve used a beta version) says: "The device halium_arm64 is not supported"

Boot into fastboot mode to solve it.

@mihai said in reflash after installing Ubuntu Touch:

I think I am in the fastboot mode : "the bootloader is unlocked and ..."

That is the normal booting process with unlocked bootloader, not in fastboot mode
To enter fastboot mode:

Make sure your Fairphone 4 is fully powered off Keep holding volume down and plug in USB-C cable to the charger/computer You're now in fastboot mode

Reference: https://forum.fairphone.com/t/no-fastboot-on-fp4-after-ubuntu-touch/96618/2