And here's a list syncing to a OPML file. Sync file is pretty flexible: Text figures can sync with md files; list, mind map, and stack collections can sync with lists in md, opml, or taskpaper files; table collections can sync with tables in md, csv, or tsv files.

And a table syncing with an external CSV file.

Here's a mind map live syncing with an external markdown file located in an Obsidian iCloud-hosted vault which is also being edited using both Obsidian and BBEdit. Notice changes from any will be instantly reflected in the others.