Think the desktop client for signal does screen share but I'll have to check first

Edit: yeah you can heres the support link

Element can screen share, but only when both users are using the desktop client. If one user is using mobile, screen sharing won't work.

https://revolt.chat/

Matrix with Element can really go fuck off. Matrix on Nheko, or Matrix on Fluffychat are way more enjoyable. I know OP already knows this but Matrix replicates the text and image chats/channels/threads/servers of Discord but doesn't have the same parity for Discord's voice chat and screen sharing.

Jitsi?

Jitsi-meet and Nextcloud Talk can do that.

Some XMPP clients can do it for 1:1 calls, but for group calls it is a work in progress and progress has been a bit slow to be honest.

There is also Element Call at call.element.io. I have not tried screen-sharing but it's worth a look.

If on mobile, maybe Signal or the FLOSS version known as Molly (Molly assuming you're on android)

I think Element works well in combination with Jitsi, well or for your need just Jitsi could probably do the job too.