I am not aware of any truly recent changes to encryption standards. I am aware TLS V1 and 1.1 are no longer supported as of Thunderbird 68.5 but that was months ago.

A check on the server would indicate it is vulnerable to hacking and is not all that secure. https://www.immuniweb.com/ssl/?id=LWLMegzl

The server also does not support OCSP stapling for its RSA certificate. Its support allows better verification of the certificate validation status. Assuming you are using V78 you can turn off this security feature in options > Privacy & Security > Certificate heading as the very bottom of the page.

For V68 Options > Security > General I think from memory.

Is it you who also reported this at https://bugzilla.mozilla.org/show_bug.cgi?id=1656742 ?

I see you answered the question asked here in your bug. That is whgat happens when you try multiple fora for support, you get confused responses.