Building your own devboard requires skills in many interdependent areas. Have you tried using an Arduino or similar first? Having built computers from TTL chips and wirewrap chassis, I can confirm that digital electronics field has grown massively and requires knowledge in many specialist areas. Even designing a PCB requires a great deal of knowledge. Tools like KiCAD are great, but they don't abstract out the requisite underlying knowledge.

A university degree in any professional field is only the starting point for a lifetime of learning. In my pre-internet days I spent several thousand dollars a year on books and professional journals all of which I read cover-to-cover. With the internet I find all the materials I need with some focused searching.

The only thing that you truly learn at university is how to research, ie ask questions and then find the answers. Being a professional means having the experience to apply your learning to specific outcomes.

For me learning is very much just-in-time. I stumble across something I don't have a clue about, so I research. Typically I come across something that I don't understand, so then I dig into that and so on. Generally I need to get down into the weeds until I connect with something I already know. Then I start building upwards. Pretty soon I hit another thing I don't understand and repeat the exercise.