Does the app upload anything to my Supernote, or change files on my tablet?
It never writes to your tablet over the local connection — the Browse & Access link is read-only, only ever used to copy handwritten notes off the device. The only changes it makes are to your to-dos (add/complete/rename/reschedule/delete), and those go through the Supernote cloud under your own account. It does not touch your documents, folders or note files.