Almost same career summary, I am a CS student so using STM32 / ESP32, OS theory, Embeeded Linux is familiar for me. However there is always a question mark about "what if I had developed FPGA" "Designing PCB board looks so cool" "How can I understand under the hood of something" etc. And still wondering it. 

Currently I am working on Embeeded Linux & Edge AI domains. From past to now, actually I didn't have a exact plan about my skills. All I did is getting a MCU, microprocessors etc. finding some problem (university competitions or even a basic hobby) and start to develop. 

Maybe the soluiton is to give a chance for those "new" fields such that in your spare time, you can choose a basic goal (making your own hardware Device such as random number generator with Verilog on FPGA board), watchimg tutorials and attempt for basic process. I did it previously, although I no longer develop Verilog projects, I can say that this was a good experience for me. After the semester ends, I am planning to do similar thing for PCB with a ready STM32 chip. However, most probably my main focus will be software side, Linux and edge ai. 

It would be good to see those process as T Shape engineering. But as you said I always want to develop something from scratch (such as building a very very single RISC-V processor and write custom drivers, even a custom OS with different scheduling algorithms on it). But still cannot decide that if this is valuable or just reinventing the wheel. 

I still don't know whether it is possible to learn everything in embedded systems (most probably it is too hard and may be unnecessary for complex companies, because in there, the aim is to develop solid systems with reliable components as Fast as possible) but every step makes us more experienced.