I looked for this and it sort of doesn't exist. I need it for a technologically challenged family member who gets hopelessly confused by smart phones. I have had the idea of writing an Android dumbify app that runs in kiosk mode (i.e. there is no way to exit it) that just disables everything except phone calls, and keeps the phone keypad permanently on the screen, like an old fashioned phone with physical buttons. It's on my infinite todo list.

A minimalist launcher is probably the easiest possible solution to that. Aster for example is available on F-Droid. The only issue I could see is it not having a lock function that would prevent them from accidentally entering some sort of edit mode.