Which features in notes are not supported prior to iOS 18.5?

The notes application and its features in iOS 15.8.4 would be substantially older than Notes in iOS 18.5 or 18.6. Apple does not publish a side-by-side list of features in either version of Notes. Trying to open a newer Note from iOS 18.5/6 with Notes in iOS 15.8.4 may not work owing to data features exclusive to the current Notes application.