If your system uses Wayland instead of Xorg, you may sometimes encounter a black screen issue when using x11grab from FFmpeg because x11grab works best with Xorg. Switching to a Xorg session should fix the problem.
If your system uses Wayland instead of Xorg, you may sometimes encounter a black screen issue when using x11grab from FFmpeg because x11grab works best with Xorg. Switching to a Xorg session should fix the problem.