What do you mean by this? Direct messages are not end-to-end encrypted, I don't know what you mean by "doesn't know how to handle". Almost every platform with direct messages doesn't have E2E today, that's the same as email, twitter, Discord... basically every other messaging platform on the web besides Signal and Matrix, for better or worse.
I remember its name (sup) but I don't really see any good updates I am not sure to be honest (https://www.notebookcheck.net/Pixelfed-Loops-and-Sup-Alterna...)