How to Reset Navigation Pane Expanded State in File Explorer in Windows 10
The Navigation pane is a special area on the left of File Explorer which shows the folders and system places like This PC, Network, Libraries and so on. You can make it automatically expand to the open folder, so it will show the full directory tree. The expanded state for the folders is saved to the registry. The next time you run the File Explorer app, it will automatically set the directory tree to the last expanded state.