About Matrix Matrix is an open protocol for decentralised, secure communications.
Matrix Manifesto We believe:
People should have full control over their own communication. People should not be locked into centralised communication silos, but instead be free to pick who they choose to host their communication without limiting who they can reach. The ability to converse securely and privately is a basic human right. Communication should be available to everyone as a free and open, unencumbered, standard and global network.
But does it have activity detection and screen sharing?
Try Mirotalk when you need simple screen sharing. It uses browser based tech so no server/app/plugin required. https://p2p.mirotalk.com/
If you delve the bridges available, some support activity, some do not
Element does have screen sharing.