User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:106.0) Gecko/20100101 Firefox/106.0

Steps to reproduce:

I was composing a new message. I had configured to sign unencrypted messages by default. I have configured S/MIME for this. After clicking send, it told me, that no encryption was configured.

It was set to OpenPGP by default.

Actual results:

error

Expected results:

It should sign the message with S/MIME.

I cannot select a default encryption in the account settings, the option is greyed out in the settings.

The workaround is to configure an OpenPGP key for the account, then you can enable S/MIME in the preferred encryption technology setting.

In a German newsgroup where a user reported the same issue this affected user reported that deleting the keys and removing secring.gpg, pubring.pgp and encrypted-openpgp-passphrase.txt also fixes the issue. The settings will still be greyed out, but the automatic selection will work. They also report that the issue started with 102.4.0 and could therefore be caused by bug 1790610. Disclaimer: Just reporting other people's findings.

This has also been reported on SUMO a couple of times.
https://support.mozilla.org/en-US/questions/1392670
https://support.mozilla.org/en-US/questions/1391906