just in case you didn’t know…and excuse me if you did.
If you need to force power off and power button on its own won’t do it, then use combination button press :
gently hold power button + vol.up, wait for 1 vibrate followed by three quick vibrations and release buttons, phone powers off.
When you have twrp installed for the first time reboot phone into twrp again even if it said no is installed. Just make sure you reboot into twrp, then flash /e/ on you phone and reboot normally. Done!
Thank you for all the replies. I got /e/os installed yesterday and everything works. Yesterday I could no longer reply because it said I had already reached the maximum number of replies for one day as a new user.
However, the fingerprint sensor is not recognized, so I can not store a fingerprint, does anyone have an idea how I can fix this?
Well done for getting eOS onto your phone!
Which os version are you currently on and was it installed at the end of that last session?
Or did you have to go back to emma?
Answers will help narrow down the options.
Currently I have /e/OS 0.13(Android 8.1.0).
I went back to Emma as I did not want to take any risks.
Good move 
Can’t help with the sensor but I seem to recall it worked on e-oreo, if a bit unreliable; had to keep resetting it. However that was back in July last year: version 0.9.
FYI:
I ran the pie testbuilds from July to the end of the year; very stable and fingerprint sensor good nearly all the way.
There should be an upgrade to Q for the XA2 early next month
Both would be best with a return to emma for 50.2.A firmware before installing.
Ok, then I wait for the Android Q update at the beginning of February.