> public/private rooms

Fully supported by XMPP: https://xmpp.org/extensions/xep-0045.html

> audio and video support

Supported by some clients (usually over Jingle) but nothing standard AFAIK: https://xmpp.org/about/technology-overview/#jingle

> threads

Rooms can have multiple threads but I don't think they're used the way they are in discord/slack/etc.

> e2e encryption

XMPP has multiple ways. Currently the most widely used by clients is OMEMO https://xmpp.org/extensions/xep-0384.html

> etc

Whatever you can think of, XMPP supports it. Whether enough clients support it for it to be reliable is another question entirely!

(The XEPs I mentioned are considered "core modern" so most clients support them, you can browse through https://docs.modernxmpp.org/client/protocol/ to see what's considered the bare minimum for a full client)