Syncing contact photos to Fritz.Fon

Hello all,
I have been running Nextcloud (now Hub 4, v2.6) in a Docker container on my Synology Diskstation for some time. So far it runs great, according to the configuration wizard I have no problems.

I had installed NC to be able to sync my contacts and calendars on my devices and to say goodbye to Google. Works also so far: cell phone, Thunderbird, Fritzbox.

However, there is a problem with the Fritzbox:
the contact pictures from Contacts (v5.2) are not added or displayed on the Fritz.Fons. I have already deleted and re-added the address books several times, also waited several nights (at night the FB syncs the phone books again). Unfortunately without success. On the cell phone I can see the contact pictures. These contact pictures are an important feature here for the family. Maybe someone has a workaround for me?

Many greetings,

no double posting please!

closing in favor of: