Getting the texture of a window when using a compositor is an nvidia specific limitation. When gpu-screen-recorder supports other gpus then this can be ignored.
Allow recording all monitors/selected monitor without nvfbc by recording the compositor proxy window and only recording the part that matches the monitor(s).
Allow recording a region by recording the compositor proxy window / nvfbc window and copying part of it.
Resizing the target window to be smaller than the initial size is buggy. The window texture ends up duplicated in the video.