Hi there, Henning_crs!
Your Quest 2's display screen remaining black after a device update is a huge hinderance when trying to enjoy the virtual world. I know how frustrating this can be when trying to use your device for fun. Don't worry, we're here to help.
Thank you for providing a list of the steps you've taken to troubleshoot your device.
Since this seems to be a situation that'll need more attention, please submit a ticket to our Support Team here.
Enjoy the rest of your day!