I had to restore my Mac with my Roon core and now it does not give me access to that Roon installation anymore as it says that I do already have another core. No. That was the version of that particular Mac prior to crashing and needing a restore from Time Machine...
Describe your network setup
Fritzbox and Fritzbox WLAN. But the issue is with my Roon Core...
It still thinks that your license is connected to the previous instance of the Roon installation on the “MacBook-Pro-von-Alejandro”. Click Deautorisieren and you will be able to choose your new, restored instance.
Great. By the way, you should not back up the live Roon database with Time Machine. Instead, use Roon’s built-in back-up mechanism (and then you can use Time Machine to back up the Roon backup). If you always have a (better: several) proper Roon backup as you should, then losing the database loses its terror because you can always restore from a backup.