This is the public test version of the new call system that you can try without an account https://call.element.io/

Its pretty new and still evolving, but this is basically just embedded in Element if you start a call in the client. From my test just now it doesnt look like you can have two people screensharing at once :( The screensharing itself works fine tho, it looks like a new share by a different person will just overwrite the previously started one.