[MarkusWandel]

For this, you really want to aim for high quality kits with high quality documentation. The typical Ali Express cheapy kit is a box of stuff with no instructions at all; you're expected to use google-fu to figure out what all the bits and pieces do and how to connect them and where to find the libraries. Which is no problem once you know what you're doing. But that's too daunting for a beginner.

Another angle is robot/robocar kits powered by Arduino, with available source code and documentation. I sent an Elegoo Penguin Bot kit to a nephew, and wrote up a blurb to get him started on hacking the software; you can see the blurb here:

https://wandel.ca/misc/robot/

The code is pretty advanced for an Arduino project, but it's trivial to tinker with and immedately see the results.