If I recall correctly, it was pretty bad. It used to open Internet Explorer on this page: http://shell.windows.com/fileassoc/0409/xml/redir.asp?EXT={e... where {ext} was the extension.
Suggestions were vague and they only made sense with well-known filetypes.
There's a screenshot of how it looked here: https://protoweb.org/wp-content/uploads/2025/08/screen.jpg
Today that page would be titled "Microsoft Windows Copilot File Associations"
The more things change, the more they stay the same.
this might be the only place where a redirection to bing provides a much better UX than what was there previously!