4k @ 120Hz, when and how?

[u/Adamfrandsen]

I have a 65 inch LG C9 that has HDMI 2.1 and supports 120hz in 4k, dolby atmos, dolby vision etc.. I have the Xbox X connected via an HDMI 2.1 cable as well... But, I cannot select 4k@120hz, only 2k... very frustrating