Well, in case anyone has the same concern. I have now been able to set up the FRITZ!Box 5590 Fibre XGS-PON on green.ch. A call to green.ch is required, they will then give you step-by-step instructions. In addition, the support will give you the access data and carry out the configuration on their site beforehand.

Hello, is your question still relevant? My Fritzbox runs with Green without any problems.

Unfortunately, we have no experience of this ourselves. However, we recommend that you ask such a question as a discussion, as experience has shown that more customers respond there than to a single question.
https://www.digitec.ch/de...