you're misreading the comment. this a about filtering the kind of notification from a single app.

notifications from a single app are split by category, and you can disable in the phone settings notifications from a single category will keeping the rest for a single app. (though this categorizing is done by the app dev not you, so the dev can mix annoying stuff with the useful)

That's not what they're talking about. On Android, notifications have a "channel". So you can disallow certain types of notifications while still allowing others through.