have you restarted your device?

Yes, multiple times.

Please check your Firewall which may be part of your Anti-Virus product.

Thunderbird must be an allowed program in the Firewall.

If it is already selected as allowed: Exit Thunderbird. then block/remove Thunderbird from list, save and exit Firewall. Then access Firewall again and set Thunderbird as an allowed program. It is possible, a new upgraded Thunderbird is not being recognised as the Thunderbird in the Firewall list. Then start thunderbird.