System update and certain apps only over wifi.

for iOS

the apps you want to restrict cellular data on need to be managed via SMC (so they need installing\managed via SMC)

you need to create an App Group containing the apps you don't want to use cellular data with.

then create an IOS policy for "Network usage rules"

add your App Group into the exception list, check the desired options and this will work to disable Data usage for the specified apps.

for iOS

the apps you want to restrict cellular data on need to be managed via SMC (so they need installing\managed via SMC)

you need to create an App Group containing the apps you don't want to use cellular data with.

then create an IOS policy for "Network usage rules"

add your App Group into the exception list, check the desired options and this will work to disable Data usage for the specified apps.