"remember" IDE configuration on Sketch

I don't know the exact technical details, but it is stored under this folder:

  • Windows:
    %APPDATA%\arduino-ide\
    
    (e.g., C:\Users\<username>\AppData\Roaming\arduino-ide\)
  • Linux:
    ~/.config/arduino-ide/
    
  • macOS:
    ~/Library/Application Support/arduino-ide/
    

I believe it is a database. I haven't figured out how to take a look at the data in there.

The data is associated with a given sketch path. It is the same system that stores the "workbench layout" (e.g., whether the Serial Monitor view is open) for a given sketch.

Yeah, unfortunately the system doesn't always work as I expect it to. I have never managed to figure out exactly how it is supposed to work. My opinion is that the developers got a bit too "clever" when writing the code: