A more lightweight option, though easier to bypass, is to disable apps, App Store, even Safari, with "Content & Privacy Restrictions". See Settings – Screen Ti

A more lightweight option, though easier to bypass, is to disable apps, App Store, even Safari, with "Content & Privacy Restrictions". See Settings – Screen Time. You can use a passcode to lock it. It seems primarily meant for blocking things from your kids. But it can help turn your iPhone more into a dumb phone (Blocking safari was the key, for me)