I actually have a solution for this if you have an old apple device handy. You can load a profile on it using Apple Configurator 2 that disables web browsing an

I actually have a solution for this if you have an old apple device handy. You can load a profile on it using Apple Configurator 2 that disables web browsing and restricts which apps can be run. (I seem to remember this working without needing a business account.) I’ve got some old devices locked into single app mode this way.