I have a Series X connected to my FV43U. I've only owned the Series X for two days, but as far as I can tell it is HDMI 2.1. I have mines running at 4K 120Hz 10bit.
How do I see if it's full chroma 4:4:4?
When you connect the XSX with HDMI ,the Display settings on the Xbox menu shows the capabilities of the monitor and allows you to choose appropriately .