1440p monitor will only run at 120Hz on 1080p

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.

That monitor supports 120hz ONLY at 1080p, and 60hz at 1440p according to the companies website. That would be why you cant select 120hz at 1440p

"With our monitors, you can run 120Hz at 1080p resolution. Or you can rock a pixel-perfect 1440p resolution at a 60Hz refresh rate. Even knowing this, you’re now able to enjoy buttery smooth gameplay
on one of the most popular game consoles of all time — thanks to FreeSync support"

From viotek website

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.

That doesnt answer the question is it going to work for older monitors that are hdmi 2.0 that didn't run at the 1440p 120hz they were supposed to run at on xbox one x i bought a viotek monitor gft27db was supposed to run 1440p 120hz over the hdmi 2.0 but
it doesn't on the one x only runs at 1080p 120hz with freesync on or 1440p 60hz no freesync will series x solve this issue thats what he wants to know i have heard it was a bandwidth issue but with the new console having higher bandwidth i would guess it would
solve the issue but would like to know for sure

the edid contains the info the xbox uses for the monitor, the monitor has 1080p @ 120hz listed and only has 1440p @ 60hz listed so the xbox cannot use 1440p at 120.

pc's can ignore the edid xbox cannot.