Wi-Fi assist cannot be turned off - iOS 14.6

Wi-Fi assist on my son’s devices cannot be turned off. The button to toggle it off is greyed out

iOS 14.6 on iPhone 12

• bell Canada network in Montreal

AND

iOS 14.6 on 6th gen iPad

• Fido / Rogers network in Montreal

I looked into Screen Time on my device where I manage a few things on my son’s devices. Nothing I can see pertains to Wi-Fi assist.

How can Wifi-Assist be turned off? Why is it blocked?