Xbox one X 4k 120hz with HDMI 2.1

You don't need HMDI 2.1 for 4k on the Series X...you only need HDMI 2.1 to run at 4k 120Hz. The Xbox One X only ran on HDMI 2.0 but it output 4k perfectly fine.

Xbox One S and X does not support 4K at 120hz and to get 4K at 120hz you need a HDMI 2.1 port on both console and TV,

also the Xbox One S is a 1080p console that upscales to 4K unlike the One X which is 4K console.

Microsoft's prior console, the Xbox One X only has HDMI 2.0. Full 120Hz at 4K requires HDMI 2.1 which that Xbox does not have.

HDMI 2.0 does not have the bandwidth for 120Hz at 4K. In any case, there are no games on the older Xbox One X that run at 120Hz (or 120fps). There is enough bandwidth for 1440P at 120Hz, which is why you select this from the menu.

Like you've said, your PC graphics card has HDMI 2.1 which is why you can use 120Hz with this connected your TV.

for 120hz you need i think hdmi2.1.

besides connecting the s at 120hz is not going to magically let it run at 120fps, you will be lucky to get 40fps on most games. kills my eyes running so slow.

HDMI 2.1 is only needed if you plan to game at 4K for 120hz , on a 4K 144hz monitor, However there's no gaming monitors available at the moment, that yet has HDMI 2.1, the first HDMI 2.1 monitors that are likely to come in are around the same time as the
Series X (Q4) launch or early 2021 (Q1),

1080p and some 1440p monitors can do 120hz over HDMI 1.4 if it's supported, but best ideally is HDMI 2.0 for 1440p for 120hz,

HDMI 2.0 can do 1080p / 1440p at 120hz and 4K at 60hz,

HDMI 2.1 can do 1080p / 1440p / 4K at 120hz.

For the Xbox Series X, it best to get a 4K TV or monitor that supports 120hz and has HDMI 2.1, to get the full potential out of the Series X.

And what if I buy a cable will it work

The Xbox Series X will come with a HDMI 2.1 cable,

But whether you use a HDMI 2.1 cable or not, the HDMI port on the TV needs to be HDMI 2.1 to achieve the 120hz refresh rates at 4K.

using a HDMI 2.1 cable on a TV port with HDMI 2.0 will still only limit the Xbox Series X to 60hz refresh rates.

[table][tr][td]Xbox Console HDMI Port[/td][td]HDMI Cable[/td][td]TV HDMI Port[/td][/tr][tr][td]Xbox Series X, HDMI 2.1[/td][td]HDMI 2.1[/td][td]HDMI 2.1 = 4K at 120hz[/td][/tr][tr][td]Xbox Series X, HDMI 2.1[/td][td]HDMI 2.0[/td][td]HDMI 2.1 = 4K at 60hz[/td][/tr][tr][td]Xbox Series X, HDMI 2.1[/td][td]HDMI 2.1[/td][td]HDMI 2.0 = 4K at 60hz[/td][/tr][/table]