PCIe provides standby power on 3.3v only. I can't find a specific number for "standby" but even not in standby it seems to be 1100mA @ 3.3v =~ 3.63W - so may be enough. You'd need a step-up to 5V for the CM4 though.

Seems like it may be borderline enough for the video part not being active but maybe similar to USB it might be "not quite enough".