Re:Thunderbird 78.x is great but has issues for advanced PGP...
by freeone3000 on Friday November 27, 2020 @12:22AM
(#25225729)
You can use a traditional smartcard to store your GPG keys. That should meet your requirements?
In fairness I also had the requirement of "is not USB" - but this is reasonable IMO (don't train your users to plug in USB key like things)