I use Arch btw.

That explains why it is easy for you. (joking)

Use netcat (nc) or similar for local unencrypted one to one chats (half joking)

My threat model is not that big :)

My dad suggested me this after i told him about the new upload filters the eu is thinking about. Here is a link to a german blog post about it: https://netzpolitik.org/2024/anlasslose-massenueberwachung-frankreich-wackelt-in-der-ablehnung-der-chatkontrolle/#dokument

Is there e2e encryption available for mattermost that normies can use?

What clients will you use for xmpp/prosody?

Sorry, but the time frame doesn’t fit. Its between 66 and 145 millenia. https://en.m.wikipedia.org/wiki/Cretaceous

The real source is on tumblr: https://slightly-awkward-sunshine.tumblr.com/post/635613714465325056/i-made-this-a-long-time-ago-and-was-very-nervous