Somehow I think when one set the display as 2160P 60Hz, it is for all playback, not only the GUI (menu).
I had it so far set 2160P 60Hz, an averythign like 4:4:4: or 4:2:2: was "SELECTED IS NOT SUPPORTSET TO BACK"... that is YCbCr420 8bit.
If I set display like I said before at 2180P 30 HZ, I can select 4:4:4:-8bit, at 10 bit is agan "bla-bla-not support, reverting ti 420-8bit.
Not 10 bit for me, also the tv manual says only 8 bit HDR. NOT 10 bit HDR
So, I think that this setting has to do with MORE than just GUI/interface/menu...
I do not have means and other intermediary devices to esteblish colorspace during playback.
Just on png image that supposedly shows good color and written detail like it were for 4:4:4: 10 bit, but definitely it is not, according to tv's documentation.
Looking forward for more suggestions.
No, the Player will auto switch the output frequency according to the video source,
that's what "24p mode" supposed to do, when it's turned on in the Playback menu. So in the case of 23.976fps video it will auto switch from 60Hz to 23.976Hz and -presuming the best case- from 420 to a 422 colorspace during playback. That's why it would make the whole "set the GUI to 30Hz for higher colorspace" concept needless. So revise my suggestions and presumptions above according to this. It's a bit still strange you can't set 444 on 60Hz with 8bit, maybe it's also because fall-back compatibility regulation reasons (I've mentioned these above), as some displays won't support it. 422 on 60Hz
just isn't on supported by HDMI 2.0 specifications, so that would be impossible with any setup. But on 4K / 60Hz / 10bit there's definitely no other choice than 420.
Edit: and like I've mentioned before, we have no clarification yet, that to what colorspace and bitdepth variation will the Player auto-switch during the Playback from various previous GUI settings. It's what one must experiment on by their selfes. It's just a presumption that -also- the best case could happen, and the switching will always result in the highest possible settings variation. In your case, settings from the GUI's 60Hz / 420 / 8bit could also end up in e.g. 23.976Hz / 444 / 8bit during Playback. And even if you set 30Hz / 444 / 8bit for the GUI, it could switch back to 23.976Hz / 422 (or even 420) / 8bit during playback. That's what we still need to clear out, as there's still not so much relevant user info is published since.
Secondly: I still recommend the 10bit option -at least- to try out on whatever colorspace is it still accepted with your TV.
e.g. My TV is a 2014 FHD modell, and it's panel is also only 8bit, but it can accept and "convert" 10bit input. So I can set 1080p / 60Hz / 10bit too for the GUI. Maybe worth to check out on your's too (But still also keep under consideration my previous post regarding TV's bitdepth "favor" and find what's works with the best PQ results for you).