In Thunderbird 91.10.0, PGP encryption appears to have multiple issues. Thunderbird has issues importing quite a few different public keys. If I try to import the file, OpenPGP Key Manager recognizes the key, shows the fingerprint, shows the email, but when you say import it says says 'Import failed'. If I try ti import from clipboard, same thing. If I try to search for them, the Keyserver can't find them even though they are available to find. If I Send an email, encrypted using Thunderbird, Thunderbird cannot read the resulting email, "unknown PGP error". But other programs using the same key Can read the same email. I've tried both to the same email and to different email accounts.