You know what? You might have actually given me the final piece of the puzzle here.
We already know the iOS 14 upgrade causes an *immense* initial draw on the battery, something that was easily the number-one complaint about the upgrade itself. Between running update processes in the background and forcing updates in the foreground, the power draw was much larger than I believe any other iOS release.
It's entirely likely that the folks at Apple anticipated this, and decided to include code to reduce power draw by other, "less necessary" elements, including but not limited to the wireless charging, USB, and camera / flash LED, in order to make the transition to iOS 14 seem like less of a problem and more overall successful. ****, I might even say that it was their intent to have the code then restore that functionality once the initial power draw boost was over. However, it would appear that someone forgot to include that, because a large number of people are still without. They fixed the camera / LED item because for many, that destroyed half the functionality of the phone, but these other issues have been largely ignored because "you can work around that".
In radio, there's a well-known thing called the reciprocity theorem, that states that an antenna's receiving characteristics are equivalent to its transmitting characteristics. The wireless charging on the iPhone is an inductive charge, but that's still a form of antenna: If power is reduced to the receiving antenna, its ability to receive is subsequently also reduced. That would explain what you're seeing, that the induction charging only works if you remove the back plate.
Similarly, USB is a signal transmitted down a wire. If the phone's USB receiver has reduced power, its ability to see that signal is also summarily reduced. So, while the phone sees the signal well enough when it's off to power itself back on, it doesn't see the signal well enough to actually consider it a proper USB connection.
I think we're getting somewhere here. I sincerely hope Apple's engineers read this, but I know it's called the "Community Forums" for a reason. :V
