Have you tried to change only the DNS Server?
Germania
On my desktop PC, which is set for static lan IP, I changed from using Comcast's DNS to Google's (8.8.8.8/8.8.8.4), and did a DNS Flush and reboot, and I still have the issue.
I also found that turning the VPN on is only needed when starting up StreamFab, once SF authenticates, I can turn off the VPN and it works fine.
This is crazy, I never had this issue before.
Oh, and I built another PC which only has Win 11 on it. It too has the same issue. Hangs on the StreamFab splash screen saying "Accessing server information" and being unable to authorize. So its not a Norton or AV issue.