Everything seems to be fine. Port forwarding is working. However in the Roon ARC app on iOS 16 I get the error “Something went wrong while syncing to your Roon core”.
Have read somewhere about some corrupted database in the past, which
might cause this problem if I understood correctly.
After 3 days of reading and “playing around” with all kind of modem settings/etc
I have installed an old backup on my Mac core. My original core is
on the IntelNuc. And it worked. The ARC connected in just seconds and
is playing without any problem since then.
So it looks like it is a database issue.