It's on my instance so it stands to reason it should be on yours as well. Make sure you're looking in the right place. It's under: Profiles > Profiles > Your profile > Wi-fi >> Disable MAC Address Randomization. It's not a device wide setting and it's a set once but leave open for user modification.

Great, got it now, thanks

iOS 14.2 update: Users can no longer manually toggle the "Private Address" setting once its managed via MDM (i.e.; the immutable flag now works properly in iOS 14.2).