Note that in RGB (4:4:4), it is not possible to output in 4:2:2 or 4:2:0 because the three layers (luminance and 2 chrominance layers) are in full format. This means that the 4:2:0 YCbCr signal encoded in a Blu-ray or 4K Ultra HD Blu-ray is decoded by the player instead of being sent in 4:2:0 and sent in 4:2:2 (or 4:4:4) to your projector, TV or external scaler (MadVR, Lumagen or other). In order to preserve the best possible quality, we favor YCbCr 4:2:2 and 4:2:0 video output signals (as far as possible according to video output standards).
Also note that in video, the YCbCr 4:2:0 format used for DVD, Blu-ray and 4K Ultra HD Blu-ray compression, is not part of the video output standards (EBU / SMPTE). The stream is therefore necessarily reconverted to 4:2:2 (of 4:4:4 if you want). Only YCbCr 4:2:0 4K UHD streams at 50 and 60p can output natively in YCbCr 4:2:0.