Advice for beginner embedded systems engineer

I've been a backend software engineer my entire career. Given the companies I used to work for, I never had the time to fully embrace my interest/passion for embedded devices. I've played around with various discovery boards, but that's about it.

I finally feel like I have the time to deep dive. I have a couple of ideas of what I'd like to do, but not many thoughts on how to get started.

Can someone experienced in designing embedded devices give some guidance/advice? Are there books/online courses you'd recommend? Is it even feasible for a hobbyist like me to design and create something from scratch? I'd really love to carry this thing from beginning to end (designing schematics, PCBs, etc etc), without using discovery boards. Any help is much appreciated!