I have tried both the Flatpak and AUR version and get the same error, it briefly shows a white screen on the display and then goes back to the connect screen. On my laptop it gives this error when running from a terminal before the connection timing out:
** (gnome-network-displays:4484): WARNING **: 14:08:29.939: Error initing screencast portal: Failed to create portal session (response: 2) ** (gnome-network-displays:4484): WARNING **: 14:08:29.939: Falling back to X11! You need to fix your setup to avoid issues (XDG Portals and/or mutter screencasting support)!
I tried posting this issue on their issue tracker but they told me to post it here first and closed the issue. If this is not a manjaro issue I’ll go back and ask again.