To mirror a new virtual display instead of the device screen:
scrcpy --new-display=1920x1080
scrcpy --new-display=1920x1080/420 # force 420 dpi
scrcpy --new-display # use the main display size and density
scrcpy --new-display=/240 # use the main display size and 240 dpi
On some devices, a launcher is available in the virtual display.
When no launcher is available, the virtual display is empty. In that case, you must start an Android app.
For example:
scrcpy --new-display=1920x1080 --start-app=org.videolan.vlc
By default, virtual display system decorations are enabled. But some devices might display a broken UI;
Use --no-vd-system-decorations
to disable it.
Note that if no app is started, no content will be rendered, so no video frame will be produced at all.