Matrix screen sharing is a feature of Element Call / MatrixRTC (in development).
replyFor now, I think they do it through their Jitsi integration. I don't know how easy it is, as I haven't tried it.
https://docs.element.io/latest/element-cloud-documentation/i...
Stoat has screen sharing / video calling in the pipeline at least: https://github.com/stoatchat/stoatchat/issues/313
replyAccording to the last comment in the issue it is already available for self hosted clients.
replyJitsi does that well
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