Hi a cant 4k resolution and 120hz at the same in my Xbox x even no my tv is a 4K with 120hz...

The Xbox One X supports 120hz only at 1440p and 1080p resolutions. It does not support 120hz at 4k. So unless your TV or monitor supports 1440p resolution (many don't), you will only get 1080p when selecting 120hz.

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Microsoft claims that:

"4K games with 120 frames per second are available if you have all of the following:

an Xbox Series X console

an Ultra High Speed ​​HDMI cable with support for HDMI 2.1

an HDMI 2.1 compliant TV

To enable 4K games at 120Hz, press the Xbox  button to open the panel and select Profile & System > Settings > General > TV & Display Options. Make sure your Resolution is set to 4K UHD and set Refresh Rate to 120Hz.

Note If you have an Xbox Series S console or your TV does not support HDMI 2.1, you can still enable 120Hz gaming at a lower resolution. To do this, set your Refresh Rate in TV and Video Options to 120Hz. If your resolution was previously set to 4K, the console will automatically adjust the resolution to support the 120Hz refresh rate. Otherwise, select a resolution among the available options."

if you set the correct settings and not the image or it doesn't reach the 4k resolution it is not compatible to run in this resolution on the Xbox X series.

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.

The Xbox One X simply isn't powerful enough to output pretty much any game at 120Hz, the console will be sending out a 120Hz image, but that doesn't mean that the game will be running at 120Hz.

Its like setting your console to 1080p but displaying on a 4K TV, the TV still shows a 4K image, but that's because the image has been up-scaled to fill the 4K screen.

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.