Hi Benjamin,
Since the error seemed to be network-related but persisted even with a fresh installation using a hotspot, I suspected the issue might be on Last.fm’s side.
So, I disconnected all linked applications, deleted my account, and created a new one. At that point, the audioscrobbler connected successfully.
I then reconnected all other applications to Last.fm, and they are now working correctly.
It looks like the issue was with the “old” Last.fm account rather than Roon.
In any case, problem solved everything is working perfectly now.
Thanks for your support! 