Nextcloud Desktop
Files & SyncSynchronize files seamlessly with Windows Explorer, macOS Finder, or Linux file managers. Supports selective sync and virtual files.
When the desktop client asks for a local folder, create a new empty one for Avigation. Do not point it at an existing folder of documents. Keep your current files where they are for now, and copy them in afterwards once the first sync has finished, so you can always tell the original apart from the synced copy.