I just got this message when Enigmail autoupdated. Anyone know how (well) GPG4Win will interact with the new Thunderbird?
Thanks
Hi Mark,
Thunderbird seems to switch to their own OpenPGP/MIME implementation,
they migrate away from Enigmail (which was using Gpg4win/GnuPG).
There was a discussion about this on the gnupg-users@ list, e.g. see here
https://lists.gnupg.org/pipermail/gnupg-users/2020-May/063664.html
If the new OpenPGP/MIME support of Thunderbird is implemented well, adhereing to the standards and the ways how it is done in practice, it will just interact fine with Gpg4win and GnuPG. 
Regards,
Bernhard