To be clear, both of these photos come from preferences in the home screen (is it called the home screen? idk attaching a photo below) of KiCad 6, not in any project or schematic preferences.
Is there something I did that caused the “Schematic Editor” section to disappear?
still there, however they belong to the “Schematic Editor” as such, it seems that you have to have the “Schematic Editor” open, for the options to be populated.
The schematic preferences section doesn’t appear in preferences until you have opened the schematic editor in your current session, but afterwards that section will be available until you close KiCad (even if you close the schematic editor). Same goes for the PCB editor and the other tools.
This is kind of just a consequence of how KiCad is architected, but I believe it will be fixed in the future version 7, i.e. all preferences will always be available as soon as you open KiCad.