The usual way to do this is to have a separate “on boarding” tab/screen that is only visible when required User Profile values are empty. On this screen, just add whatever input components and other messaging you need. Let’s just say for example you need their name, and their favourite colour. You could create an if-then-else column in your User Profiles sheet something like:
If Name is empty, then null
If Favourite Colour is empty, then null
Else true
And then set the visibility of your onboarding tab to only show when that if-then-else column is not checked. And if you want that to be the only tab they see until they’ve completed their profile, then you could set the inverse visibility on all other tabs.