Why does the App Store keep disappearing on my son's iPhone?

Usually on my sons phone, app downloads are not allowed. When we changed the settings to allow app downloads in the screen time settings, it appeared briefly, even letting me open it, before closing and disappearing again. This happens every time we toggle the setting on and off. It is not in the App Library, and you can not find it when you search. You can actually watch the app disappear from the screen after a few seconds when you change the setting to “allow”. This started after the most recent update, so I am assuming it’s a glitch. How can I get the app store back?

[Re-Titled by Moderator]