Good morning. In my opinion the best solution to this problem is the following.
1080p(BT.709)@any frame rate: YCbCr 4:4:4 10 or 12 bits Bt.709 output
2160p(BT.709)@23.976hz, 24hz, 25hz, 29.97hz, 30hz: YCbCr 4:4:4 10 or 12bits BT.709 output
2160p(BT.2020)@23.976hz, 24hz, 25hz, 29.97hz, 30hz: YCbCr 4:4:4 10 or 12 bits BT.2020 output
2160p(BT.2020)@50hz, 59.94hz, 60hz: YCbCr 4:2:2 10 or 12 bits BT.2020 output
I wrote 10 or 12 bits because i dont know the highest bit depth vero 4k can upsample. Everything should be played back according to the source’s colorspace. No conversion. Except for when a BT.2020 video is playing and the tv/projector/display cant handle hdr and the player needs to convert to sdr. The gui can be in 1080p bt.709 60hz 8 bit. If it can go up to 10 bit or 12 bit ( still 1080p bt.709) without messing the table i posted above is an added bonus. Less banding.