Try installing
manjaro-pipwireif you don’t have it.
The behaviour of my browser seemed to have changed, and no longer lets me share a screen. I end up with a presentation of three black screens to share, and no one gets to see the full screen. I also noticed some missing applications for sharing a window.
Searching the net, I found a Google Chrome option that enables sharing using pipewire. As I’m using Manjaro Gnome under Wayland this probably needs enabling.
or more specifically:
vivaldi://flags/#enable-webrtc-pipewire-capturer
Once I enabled this, my share options changed, and I can now select the entire screen or the missing windows.