Im doing software engineering now, but did my undergraduate in ECE.
ECE is quite broad. It covers signals & systems, electricity and magnetism, basic circuits, embedded devices, to name a few.
What area are you interested in?
Its going to be hard to learn all without a degree, but pick a subarea.
How low area are you considering?
Embedded shouldn't be a giant transition. Fabricating transitors is a whole other level
Where do you intend to use it? I have an older Fire tablet that, while never fast to begin with, is frustrating slow. Ive been using it to remote into my desktop, and want to experiment running linux/windows/android/chromeOs or something in a VM and rdp into it.
Its going to be hard to learn all without a degree, but pick a subarea. How low area are you considering? Embedded shouldn't be a giant transition. Fabricating transitors is a whole other level