GNOME Remote Desktop works for me just fine in system mode:
Headless Remote Desktop setup process - #2 by vgaetera
To apply config changes, be sure to restart the service:
sudo systemctl restart gnome-remote-desktop.service
If the problem persists, check the service status, sockets, key and cert, credentials, etc.:
systemctl status gnome-remote-desktop.service
sudo ss -lnpAinet | grep -e gnome-remote
sudo grdctl --system status --show-credentials