Why am I unable to play 1440p120fps with a monitor that supports it and I have a hdmi 2.1...

Hi,

Could you provide the exact model?

I've done my own bit of research, but the fact that I can't access the official manufacturers website doesn't bring me much hope. Your display isn't HDMI 2.1, or at least my searches suggest it isn't. This itself does not prevent 120Hz via HDMI on a 1440P display, but if it was HDMI 2.1 it would would have had a better chance of supporting it.

Most gaming monitors, especially the older models, are designed and marketed towards PC gaming. PC gaming is primary used via Display Port and monitor manufacturers largely put all of their display's features on the Display Port. HDMI is a secondary concern.

In addition, there is also an issue with timings. For the Xbox, the exact refresh rate timings are all important. With your monitor connected to your console, the Xbox reads the displays EDID and this tells your console what the monitors capabilities are. You likely can't choose 1440P 120Hz because unfortunately, your display can't do 1440P (2560x1440) @120Hz over HDMI. This is quite common on older monitors.

The monitor released back in April 2022, it’s called KOORUI 27 Inch Computer Monitor, QHD 2560P Gaming Monitor 144Hz(1ms, 1800R Curved VA Panel, DP1.2+HDMI*2, Build-in FreeSyc, Compatible G-sync, Narrow Bezel with Ultra-Thin), Tilt Adjustable,Eye Care

The monitor is a 1440 144hz Monitor with HDMI 2.1 which is compatible for 1440p 144hz which is the Native resolution.

Your Monitor only uses HDMI 2.0,

There are no Monitor's available as of yet that supports HDMI 2.1,

The very first Monitor to support HDMI 2.1 ( The World's First Monitor to have HDMI 2.1 ) won't be released until the end of December if it doesn't get delayed and that's a 4K 144hz Monitor.

Thank you again, last question, will the xbox series X be able to support 144hz for monitors?

No, they will be capable of 120hz over HDMI 2.1 if you have a monitor with HDMI 2.1,

But, as of yet, there are no gaming monitor with HDMI 2.1,

The first gaming monitors to have HDMI 2.1 wont be available until the end of this year to early 2021.

so i am trying to use 120hz with 1440p, the monitor handbook says it it supported through hdmi, and i know that it’s an xgaming monitor. might i need an hdmi 2.1 cord?