Hi Lucas,
Out of curiosity, did you disconnect the battery when you changed the screen?
It's a long shot, but the reason I ask is that I had a similar experience with my niece's Pixel 4 XL. Her phone died; no reaction to being plugged/unplugged and no combination of any button presses did anything. Just totally gone; not even the charging display you got.
I told her I'd take a look at it, and once I got it I opened it up and disconnected the battery while I poked around for a half hour or so. Couldn't find anything wrong, so I plugged the battery back in and to my surprise the dang thing booted just like nothing was ever wrong with it. After much testing and checking everything was fully functional so I buttoned it back up. Since then it's been working to this very day.
Literally the only thing I did was disconnect the battery for 30 minutes or so. As I mentioned, it's unlikely to fix your problem but if nothing else is working maybe it's worth a try.