Even worse, I want to eventually transition into, not only a different stack, but to a different subfield altogether. The odds are likely stacked against me, but I have a few strategies to try to make myself more appealing to employers.

What I don't understand is, let's say I'm a web developer with say a decade of experience, and want to do something different (ML, embedded, game dev, etc.). Do I need to look for entry level / junior jobs in the field I want to move to, because although my 10 years of previous experience isn't completely useless, it's significantly different.