I use the screen sharing feature on discord to watch movies with my friends but I would prefer a FOSS alternative. I've tried Element/Matrix with the Jitsi add on but it seems like you can't share the audio using that and the app can be a bit buggy in general. Does anyone have any other recommendations?
As far as I know Matrix is the best FOSS alternative to Discord right now. Maybe try using the coturn addon for voice instead of Jitsi. I've been able to share audio snippets just fine this way.
If you're watching movies with friends and want a FOSS alternative, Jellyfin is the way to go. It's basically a way to host a media streaming center that others can connect to. It might be a bit overkill depending on your needs, but it's great for that exact purpose. It doesn't have chat or anything, though, so you'll want to keep something else around for that.