That is often a limitation of your cable, or your television. In the event you’re utilizing the Xbox HDMI cable that got here with it, it’s not a cable difficulty. It’s a HDMI 2.1 compliant cable.
That is more than likely a television difficulty.
First, double examine your television has an HDMI 2.1 port. HDMI 2.0 can not can not do 4k/120. Solely 4k/60 or 1080/120. Second, in case your television does have an hdmi 2.1 port, ensure you don’t have to put your television in Sport Mode or some comparable setting some early adopting 4k/120 tvs would solely do it with sure settings off or switched to sport mode.
You’ll more than likely have to confer with you television handbook, or look the mannequin quantity up and analysis on-line.
I hope this helps!