This feature has been added in Android 11 but you have to enable developer options to enable this feature. Below are all the steps you need to follow to enable the refresh rate options in the Developer options.
Steps to Display Refresh Rate on Android 11
If you want to disable this feature in the future, you can disable it from the Developers options. To disable this feature, you can go directly to the Developer options, you don’t have to enable developer options again. Also, read | How to Use Built-in Screen Recorder in Android 11
Wrapping up
This is how you can enable refresh rate counter on the display of your Android smartphone running the Android 11 Beta. You can confirm if the refresh rate your smartphone supports is working correctly or not, this will be good feedback for the developers of the Android 11.