Since a couple of weeks I can’t add new TV shows, I always get a message “Can’t connect to TheTVDB”
Is this still an issue? I’m not aware of any outages at https://www.thetvdb.com
Did you try on another network (WiFi, mobile data, etc.)? If you use a VPN, proxy or ad blocker, try to turn them off.
edit: OK, got a few reports via email over the last few days (I was on holiday). Pushing an update today or tomorrow which might resolve those issues.