We did this with our kid, no smart devices in the back seat. We didn't make sure she had something to do at all times. Most of her toys were (and still are) stuff that need some creativity and imagination (just wooden blocks, Legos etc.)

Now she can sit in the back seat for an hour, just staring out the window thinking about stuff. She seems to be able to play with just about anything, any object can be a source of play and games for her.

Creativity and independence in thinking comes second.

That's probably the worst you can do to a child. It's setting them up for unhappiness.

It's typically parents who nominally want their children to become " independent and creative thinkers" who setup a curriculum with music school, dance lessons and foreign language courses.