Can the original xbox one run 120hz

It's the same game but now running at much smoother frame rates with an option to turn on Ray tracing in the form of more realistic RT shadows.

Or, if you own modern TV or monitor you can play in 120hz mode which is a night and day difference to the original Xbox One version.

The thing is if i go into xbox tv sertings i can set to 1080p 120hz. Do i actually get it?

No. your TV display needs to support 120hz to get 120hz from the Xbox,

your TV is limited to 60hz, so that all you'll get, unless you upgrade your TV to one that a true 120hz display.

There's no possible way to get a 60hz display to run at 120hz.

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.

To take advantage of 120Hz, you'll need an Xbox One X or Xbox
One S running the Xbox May 2018 Update. So as far as the original Xbox One it sadly is not a possibility.

It sounds like any monitor that uses non standard Vesa frequencies (144hz as opposed to 120hz) will not be able to effectively run at 120hz with 1440p on xbox one x.