I could condense that down to a single task that will get you 90% of the way there: Learn how to bit-bang a serial interface on two different microcontroller platforms.
Also, does FPGA come to mind when embedded is mentioned? I always assume that FPGA is a whole another subject (only FPGA not the board part).
This has been my assumption as well. I looked a while back at learning FPGA development because it seemed rather interesting, but quickly decided to go another route after seeing and talking to some FPGA guys. From what I saw it does not in any way resemble what I'm used to as a software developer
I say this all as a "full stack" embedded guy. I'd love to have someone else take on part of it, but I'm a solo consultant right now :). Did both EE and CS in school, and more than happy to do whole projects end-to-end, but I also don't expect EEs to be fantastic programmers, or embedded software people to be fantastic hardware designers.
I was talking about embedded development which doesn't really have anything to do with PCB design, power, FPGA, etc. You don't need those things to be a programmer working on embedded systems or microcontrollers.
Implementing a serial interface in software flipping GPIOs up and down will expose you to a whole lot of the necessary ecosystem and if you can do it, you're well past the point where you should be able to get paid to do it and the point where you need a roadmap to tell you where to expand your skills. I didn't say doing it would get you a senior level position or a masters degree in EE.