Ah I see you work in a bureau of the German government where fax machines are still the standard of communication. Emails get printed out and faxed over.
However it is a very small library. The idea is good but with under a hundred books it is not really an library. (at least it was that when they mentioned it in the news a few years ago)
For revanced I can say it must be a change on Youtubes site. Because I had the same issue with a relatively new Version of Youtube and revanced on Android 12.
There is the new app grayjay.app which might be a solution for you. YouTube flagging your account is a risk you probably already take with revanced