Remove button is greyed out for the particular application in the Application Portal:
Uninstallation command is not specified for the particular deployment.
Please navigate to SCCM Console > Software library > Overview > Application Management > Applications.
Select a specific application and proceed to the Deployment types > Right click on the actual deployment > Properties > Programs tab.
There you will see the installation command line:
To specify the command that you want to use to uninstall the application on a Mac, please add the uninstallation command line, using the following syntax:
:<Installation command>:<Uninstallation command>:
The <Installation command> and <Uninstallation command> parts should contain the installation and uninstallation commands respectively.
Please note that the installation command gets populated automatically, unlike the uninstallation one.
You have to find out what the actual uninstallation command line for a given application is yourself (however, this is just
rm -rf for the majority of programs).
As an example, the following command line contains the installation and uninstallation commands for Firefox (please note the colon characters, which are required - all three of them):
:/usr/bin/ditto "Firefox.app" "/Applications/Firefox.app":rm -rf "/Applications/Firefox.app":