Confirm the underlying file is available

  1. Open the folder in Finder and try opening an ordinary note.
  2. Choose File > Open Notes Folder in MarkThatDown and select that exact folder again.
  3. Check a known note and make a small reversible edit in a test file.

When the folder is on an external or synced drive

Connect the drive or download the needed files. Check the provider’s status. Avoid moving the whole folder while an editor still has unsaved changes.

Grant access to the chosen folder

Do not grant broad disk access merely to fix a selected-folder problem. The app works with files and folders you choose.