This feature is available to participants using Firefox and Chrome/Chromium (I didn’t test others).
The side that will be controlled needs to run the Jitsi Meet Electron desktop application available for GNU/Linux, macOS and Windows (scroll down to Installation).
Note : You can control another desktop but you can not share control of your desktop if you are using a web browser to access a Jitsi Meet meeting.
Once participants are in a meeting, at the top right (tile view) or bottom left (thumbnail view) of the other participant menu, below Kick out and Mute you will see another option, Remote control.
The remote participant will get a request to approve the remote access request. Only then will it be possible to control the remote screen.