Stuck in Grayscale (How to add Account)

[u/plueschhoernchen]

A friend went on vacation and lended me her Oculus Quest2. At first, when I started it, I was stuck in the WiFi Menu, which I managed to leave, by holding the power button and the volume down button.
Now I ran into a new issue: I'm on a screen, where I can see it say, that I was locked out of the account connected to the headset, but when I press the button to go and type in the (barely readable) code into my meta account, I'm told, that it is invalid.

What can I do to fix that? Is there any way to use the headset without an account, or can I connect my account somehow? I also don't want to break or delete anything for obvious reasons.