How to Stop iOS Software Updates Using Cellular Data?

I use celular data at school because they block certain cites and apps while on the premises. When I get home I go back on wifi. I have an iPhone 8 and automatic updates turned on. I heard that it is required to have wifi to auto update with anything lower than an iPhone 12. Can someone help me understand how a software update ate through half my data?

There must be a setting im not aware of unless someone completed a software update while on hotspot.