Comment 5 for bug 1698270

This happens in full-screen mode for a window with client-side decorations using OpenGL. Another workaround is to use GNOME MPV without CSD or without OpenGL: https://bugzilla.gnome.org/show_bug.cgi?id=778766#c2

Re comment #2: With GNOME MPV, it doesn't happen on KDE Plasma for me even if both CSD and OpenGL are enabled.