It can be enabled, go to Settings > About phone > System information > build number (tap 7 times) go back to settings and you will find it at the bottom.
Please try clearing the system cache and rebooting your device.
If issue persists, please send us an error report with screenshots from One UI Beta App (Beta Feedback -> Send feedback-> Error Reports -> "Select Category" -> Input frequency and Description" -> Send (Top Right Icon). We appreciate your help for supporting beta program.
