Thunderbird has been updated to version 78.
However this version was not meant to be published by distributions because it deprecates the Enigmail addon and the integrated OpenPGP feature is known to have bugs.

I have run into such a bug now and am unable to open any messages in my inbox because every message gets automatically encrypted by my mail provider.

I filed a bug report here and there is a hotfix available now:
https://bugzilla.mozilla.org/show_bug.cgi?id=1653651
The hotfix is here:
https://phabricator.services.mozilla.com/D84045

Please apply this hotfix in the thunderbird package and publish the new revision.