Add known issue about "Edit locally" for file provider

user_manual/desktop/macosfileprovider.rst

@@ -153,11 +153,28 @@ stores that information locally, so all subsequent opens will work correctly.
 To avoid the issue entirely, right-click the alias file in Finder and choose
 **Keep Downloaded** before opening it for the first time.
 
+Edit locally
+^^^^^^^^^^^^
+
+The :guilabel:`Edit locally` action offered by the Nextcloud web interface
+cannot open files that are managed by the File Provider extension.
+
+This is a restriction of macOS itself, not a fault in the client. For your
+protection, macOS only lets specific apps open a given file, and it does not
+allow an app to grant itself that permission. The part of the client that is
+allowed to manage these files is not permitted to launch other apps, and the
+part that could launch your editor is not permitted to open the file.
+Granting Full Disk Access does not help, because a different part of the
+macOS security system is responsible for this.
+
+To edit such a file, open it directly from Finder instead: select your
+Nextcloud location in the Finder sidebar and double-click the file.
+
 Troubleshooting
 ---------------
 
 Debug-level Logging
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+^^^^^^^^^^^^^^^^^^^
 
 Debug-level log entries for the File Provider extension are disabled by
 default.