Just upgraded to 5.8 after some drama with phone rebooting when upgrading.
Anyways I am no longer able to just sign outgoing emails. I can fully encrypt the email without problems.
I have not been able to locate a setting that would allow me just to sign emails.
You might have to turn off Settings > [Account] > End-to-end encryption > Hide unencrypted signatures.
If it is enabled, signed-only messages are displayed like regular (unsigned) messages. The assumption is that you then don’t care about sending signed-only messages either.
Interesting. It used to be a global setting and now it’s a per-account setting. Upgrading from 5.600 to 5.800 should have migrated the data from global settings to all accounts. However, the settings import code currently doesn’t support doing something like that (and so the value of the setting is lost and the default is used instead).