> Here is a simple example: using a few discrete parts, like two transistors (Darlington pair), a LED and resistor, you can create a simple circuit that shows varying brightness of the LED depending on how close you move your hand or an object to an antenna connected to one of the transistors (forming a sort of proximity sensor)

Do you have some book/video/etc. recommendations for this "type" of Electrical/Electronics circuit engineering? I only know how to program a MCU :-(

There were excellent boxes and manuals to get started with electronics for children and teenagers a few decades ago. I don't know how the situation is today but maybe it's worth looking for that. Here in Germany there were sets that had excellent accompanying material that went as far as creating different types of radio receivers.