On my pc screen it shows:
daemon not running; starting now at tcp:5037 daemon started successfully List of devices attached A209xxxxxxxx device
So I do:
fastboot oem unlock 6bxxxxxx
and I get on the pc screen:
< waiting for any device >
and my phone is showing the following picture!
The solution I got on the forum of Fairphone was:
“Maybe you need to run it as root”
And that solved my problem.
Normally one doesn’t work as root on Linux, only as user.