Microsoft- 1440p 120Hz not working!?

thx for your fast reply. Ok I understand, but why is it working with 1080p and 120hz ? But not with 1440p and 120hz?

I just purchased the same monitor and am having the same issues

I'm having the exact same issue with my monitor. It's a Dell S2719DGF, supporting up to 2560x1440 at 144Hz over HDMI 2.0. I've tried an assortment of settings and HDMI wires; I even purchased an HDMI 2.1 wire to see if it was a bandwidth problem, eventually
coming to the same conclusion as you... It's a problem with the Xbox. I can run 1440p 144hz with Freesync/G-Sync enabled perfectly fine over HDMI on my PC with my RTX 2070. For now I'll be forced to stick with 1080p 120Hz until Xbox releases a fix, or addresses
the issue.

I Have tried these steps with no resolution to the problem.

1. Factory Reset x 2

2. HDMI 2.0 Cable x 4 capable cables

3. HDMI 2.1 Cable capable of 48gbps

4. Enabled 4K through Xbox menu. (Unable to upscale as it wont allow 4K 60hz or 50hz, but will allow 24hz).

5. Every possible menu combination through display.

Findings

1. Will display 1440p @ 60hz and variable refresh on.

2. Will display 1080p at 120hz, but not simultaneously with variable refresh on.

3. Can select 4K, but only at 24hz.

4. Monitor will accept 1440p 120hz through all mentioned cables from GTX 1080Ti on my PC.

5. Can not increase reduce monitors refresh rate through monitors settings.

Equipment

1. Xbox One X with latest firmware update.

2. MSI Optix MAG27CQ 1440p 144hz VA Panel

Conclusion

1. The Xbox is the issue. The Xbox does not recognize the monitors refresh rate correctly.

2. Microsoft needs to address this in two ways.

1. Informing the consumers about the issue. Its common enough and microsoft has not gone public to the consumers.

2. Find a resolution to the issue and include it in an update.

Hi there MichealHeidelberg

So you got a new monitor to try to use it xbox one X and it is only allowing the 1080p. Sometimes there is mointer issues, I can looking up this current monitor to check issues and other possible issues. Please make sure you have went into video settings
of the xbox one X to try different settings due to some Monitors can be funny with certain settings.

Edit: I have emailed the makers of the monitor to double check that there monitor can be supported by this, It might be a simple case of 1040 is the highest due to frequency and no software to tune it to highest which normally happens with PC.