Clarifications for a newb

[GrumpyGiuseppe]

I used DisplayCAL for calibration and my monitor has about 85% P3 coverage.
If I understand it correctly I can either choose to clamp to sRGB to see the content like the creator or clamp to P3 to stretch the content to P3 but both would be equally accurate and I don't loose details.
I ask because with P3 it's easier to spot differences in games in my opinion.

My TV has a HDMI 2.1 port but is connected to a RTX 2060s which only supports HDMI 2.0.
Do I need to calibrate in 2560x1440 and RGB or in 3840x2160 and 4:2:0 if I want to use 3840x2160 later?
Only the refresh rate of 120Hz needs to match it seems.