My issue is really summed up in this picture:
TL:DR: Android Studio's Device Manager can see my phones (one physical and one virtual), but neither of them appear in the dropdown at the top to let me run my Flutter app.
full: I just had to reinstall windows because of a failing SSD. I have installed Flutter, Dart and Android Studio following the same instructions that I had a few months ago when I first started learning Flutter.
This physical device worked to debug Flutter apps before I had to reinstall windows and still works to debug non-flutter android apps via Android Studio, so I know that the device's Developer and USB-debug settings are correct.
I have followed Google's instructions to update both my Windows and Android drivers (using the tools in both windows update tool and Android Studio>File>Settings>Appearance & Behavior>Android SDK>SDK Tools>Google USB Driver)
I have restarted both the software and the computer itself.