The screen is black
The session connected but there is nothing to see. Almost always a display problem, not a network one.
Screen sharing copies a real display. If the far computer has no display, or the system is blanking it, there is nothing to copy.
The giveaway: the toolbar says Connected and the numbers move, but the picture stays black.
Windows
No monitor plugged in
Fit an HDMI or DisplayPort dummy plug. It costs a few pounds and makes the machine believe a monitor is attached. This is the reliable fix.
Locked, with no monitor
Windows blanks the display about a minute after locking a machine with nothing attached. Sign in once at the machine, or use the dummy plug above.
A game running fullscreen
Fullscreen exclusive mode can hand over black frames. Set the game to borderless windowed.
Linux
- The host service must run inside an X11 login session. Pick Xorg at the login screen, not Wayland.
- With no monitor, you need a virtual display from your graphics driver, or a dummy plug. RealFrame does not create one.
echo "$XDG_SESSION_TYPE" # want: x11
systemctl --user status realframe-hostmacOS
Missing Screen Recording permission is the whole story. Without it macOS lists the display and then hands over zero frames, which looks exactly like a network fault.
System Settings ▸ Privacy & Security ▸ Screen Recording, switch RealFrame Host on, then start sharing again. See macOS.
Before you put a machine away
Set it up while you can still see its screen, then check you can reach it from somewhere else before it goes in a cupboard. See computers with no monitor.