what do I do if I do not see the option “refresh rate” in “TV & display options?

On xbox one x you can access it in settings > general > TV & display options.

Within this screen there is an option to alter the refresh rate, however this will depend on what TV setup your Xbox picks up and what refresh rates and resolutions it supports.

To allow video apps to support 50Hz when 50Hz content is displayed you can from the same TV & display options screen go into advanced > video modes.

In this screen there is a checkbox (if your TV supports it) that you can check so then it will automatically enable it when required.

I understand to try the procedure to follow, please.

After connecting the cable to your Xbox and your monitor, go to your Xbox display settings and set Overrides for HDMI ( General > TV & Display Options > Video fidelity and overscan). After doing this, the screen should display a resolution of 480p and a new dropdown list for refresh rate should appear in the TV and display options menu. After that go back to the resolution settings and change it to 1080p and refresh rate to 120HZ.

To confirm that the console is at 1080p 120HZ, look at the monitor's system information menu (Menu>System Setup>Information.

How do I check if my tv runs HDMI 2.1?

I can’t change the refresh rate. No option to change it. My FPS is 60

Had this problem contacted vizio and I had to uncheck the allow variable refresh rate in tv&display options on the Xbox one x and also had to turn off variable refresh rate in the pro gaming engine in the advanced picture settings.

Hard to tell whats going on with no information. Consider trying the following:

• Configure the console for 4K/60 with VRR by going to Settings> General > TV & display options > Video Modes >
  check the box for Allow variable refresh rate.
• Configure the console for 4k/120 with no VRR by going to Settings > General > TV & display options > Video
  Modes > uncheck the box for Allow variable refresh rate. The resolution and refresh rates are found under “Display” in TV & Display options.
• If you wish to experience 120hz and VRR, please configure for 1080p/120hz VRR or 1440p/120hz VRR by Settings > General > TV & display options > Video
  Modes > check the box for Allow variable refresh rate. The resolution and refresh rates are found under “Display” in TV & Display options.
  

If you are experiencing a corrupted image, here are your workarounds to reverting back to a safe video mode:

• Restart your console and configure your video modes to one of the listed options above.
• If you're still experiencing a corrupted image after restart, disable VRR on the TV. Please consult your TV manufactures on how to do this.
• If the issue still persist after steps 1 and 2, perform the video mode reset sequence to get back to a safe state and configure for one of the two options above. To do this, follow
  the steps on this page here under “Your screen is blank after you turn on the console > Reset your display settings”.

If you still have issues, reply with the console your on, the tv model, a game you're trying to play. The more information we have, the better someone will be able to help you.