You want to know why there isn't the ability to select Application File Access for Read Only with MacOS.
In the Enforce console navigate to System > Agents > Global Application File Monitoring, then select on an application and you will see at the bottom of the page
Release : 15.8, 16.x
We manage Windows and MacOS operating systems differently.
With MacOS operating system we manage file read and file open operations as the same. And, we can't separate them like we can on Windows.