pixel 4 - what part likely broken?

i have an old pixel 4 that i have used as a secondary phone, so i don't always use it. i left it on a low wattage wireless charger for several days and came back to it completely bricked. I've left it for similar or longer before with no problems.

The phone doesn't do anything at all. pressing the button does nothing. no failed boot, or any activity at all. neither wireless nor wired charging does anything. I've tried leaving it unplugged for an extended period to let the battery drain then plugging it in again and still nothing.

i was going to just recycle it but then i thought it's a good opportunity to practice repairing it. but I'm not sure what is the most likely part is the fault.

realistically I'm only going to try it once, if it's not fixed I'm not going to try other parts since i don't actually need to fix it, just using it as practice. but it's still nice if i do manage to fix it.

so i want to maximize the chance that i get my one shot right, and order the part that is most likely to be the culprit.

my first guess is that it's a power issue, both because of me leaving it on charging for periods at a time, and also because it having no activity whatsoever. and also it's probably the best likelihood-to-cost ratio

but i see that ifixit sells both the battery and the usb charging board. i can't decide between the two. on one hand, neither wired nor wireless charges, which suggest something common between the two. on the other hand, if it's only the battery i would expect that it at least boots up while plugged in and just doesn't charge up.

or maybe it's neither of those at all?

anyone have suggestions about the most likely part that is broken in this scenario?

thanks!!!