User Configuration > Administrative Templates > Microsoft Word 2016 > Word Options > General
User
HKCU\software\policies\microsoft\office\16.0\word\options
This policy setting allows you to hide the modern comments opt-out toggle in Word from your users. Note: This opt-out toggle is only temporary and will eventually be removed from Word. If you enable this policy setting, the toggle to turn off modern comments will be hidden from your users. If you disable or don't configure this policy setting, your users will be able to temporarily turn off the new modern comments experience from the Options menu in Word. Note: This policy setting only applies to subscription versions of Office, such as Microsoft 365 Apps for enterprise.