That's a good question. A portion of the exam is just FCC rules & regs and operating procedures. That stuff is, IMO, fine to "just memorize" because there isn't much theory to begin with. The main part where there is some theory (at the Technician level) is some basic knowledge of electronics and just a hint of some stuff that would probably be covered in a Physics 101 course (electromagnetic radiation, frequency spectrum, etc.). I don't know of one consolidated course that covers that from a ham radio perspective specifically.

In my case, I'd been dabbling with hobby electronics for nigh on 40 years when I took my test, and was always a little bit of a physics geek, so I mostly just had to learn the FCC rules and procedures bit. The downside is, since my knowledge was cobbled together from many sources over many decades, that I can't give you a good reference to a nice, consolidated, comprehensive course on this stuff.

That said, here are a couple of books that might be useful for picking up some of the theory, without going overly deep. Also note that "going deep" isn't a Bad Thing, especially if you want to progress beyond the Technician level license, as the subsequent exams do require deeper knowledge on some of the electronics/physics theory stuff. You don't have to be an EE or a physicist to do any of this of course, but just be aware that the theory component does increase a bit as you progress.

https://www.amazon.com/Understanding-Basic-Electronics-Softc...

https://www.amazon.com/Radio-Theory-Handbook-Beginner-Advanc...

https://www.amazon.com/How-Radio-Signals-Work-Sinclair/dp/00...

https://www.amazon.com/Basic-Communications-Electronics-Jack...