[Anarch157a]

I don't know if this is a feature of Android or of the alternative ROM I'm using, but I can disable network access on a per app basis.

In my Android Pie based ROM, in Settings / Network & Internet / Data Usage / App data usage I can select any app and disable WiFi, Cellular data or both.

[angry_octet]

That must be the custom OS build. Many official builds allow you to disable cellular, though very time consuming.