If I run steam with -pipewire-dmabuf and steamvr beta, I get desktop streaming by going “stream vr without a game” and then selecting desktop in the Frame taskbar.

Edit: looks like desktop streaming is fragile though, switching away from the desktop and back later in the same session resulted in an empty frame with no image again

I’m not sure about intentional desktop mirroring, I’ll have to look into that, but it does allow Steam to stream the desktop when games show a popup or launcher window instead of starting. I’m fairly sure that without that option all I got was an empty frame in the Frame.

For the desktop mirroring, if you are using Wayland, have you tried starting Steam with the -pipewire argument? Seems to be required for me for Steam to request the necessary permissions to capture the desktop for streaming.