You don't need DOS or a Raspberry pi to learn tech. What you need is the right mindset and a desire to tinker. If your kid is "bitching" they simply don't care to learn about tech. Don't force it down their throat as that is not going to end well.

They are interested they will learn by simply tinkering and playing around. You should avoid giving them guidance as that doesn't teach critical thinking. Let them figure out how to do whatever. It might be improving the frame rate in Minecraft or it could be doing some sort of programming project. It could even end up being desktop customization or digital art.

I also think it is perfectly reasonable to tinker with a mobile device or tablet. You can do all sorts of things especially with some of the apps from F-droid such as Termux.