Filing is never final. Moving a note is quick on both platforms, and nothing about the note changes except where it lives.
On desktop
Drag the note from the list onto a folder in the sidebar. The folder highlights as you hover it. You can also right click the note and choose Move to Folder, which opens the folder tree including subfolders.
On mobile
Swipe a note row to the left and tap Move, or open the note and choose Move to Folder from the header menu. The folder tree appears as a sheet, and folders themselves can be moved the same way, including up to the top level.
Moving many notes at once
Moving works note by note. If a whole batch belongs somewhere else, it is often faster to move the folder itself, or create a subfolder and move the stragglers into it one at a time.
Links and tags survive the move
Note links keep pointing at the right note and tags stay attached, so reorganizing does not break anything.