Won't Turn On Despite Good Battery

I have a Kindle Fire HD 10 9th gen which is pretty new. I usually used it for video calls that lasted more than half a day, every day. I'll admit, I would often keep it plugged in for much longer than necessary to charge it. It had recently begun to decrease in battery life, often turning off when it showed 10%. So, I wasn't exactly surprised when I came home one day and found that it wouldn't turn on. No sound, no visuals or battery symbol, nothing.

I tried to hold the power button, tried to keep it plugged in for a few hours and then attempt to turn it on while it was plugged in, tried to hold the volume and power button at the same time, and even tried to hold the volume up button to then hold the power button for 45 seconds and continue to hold down the volume up button. No response noted during any of that. I opened it up to take a look at the battery which I assumed was dead, however I was able to get a reading of 3.4 V with a multimeter on the 3.8 V battery from where the it connects to the motherboard (obviously with it unplugged from the board). This makes me think that the battery is actually not the problem. While I had it open, I tried to listen for any changes while I played around with the power buttons and volume buttons, trying all the steps I had before. Although I was able to hear something coming from the device, I didn't notice any difference while I was pressing any of the buttons down.

At first this led me to believe perhaps the display is bad, but that cannot be because I would hear the thing turning on audibly. I'm interested to test the other components to test where the failure is but I'm not sure what to test. Any ideas what's wrong with the device? Am I wrong in believing the battery is good due to the voltage readings I'm getting?