Borosocsi True, but there is no 'sorting' of songs in a Playlist. The construct of a Playlist (rightly or wrongly) isn't designed for that. You 're-order' a Playlist and that is a permanent operation (https://stagetraxx.com/docs/v4/library/playlists/#reordering-songs)
So, if the problem is "how can I break my 1,000 songs into smaller groups based on certain criteria AND THEN be able to further sort/filter" then Playlists are not really the answer. Folders and keywords are the better option, but admittedly still not perfect. Feel free to create a new feature request (https://support.stagetraxx.com/d/4778-how-to-write-a-good-forum-post) if you have a scenario where you feel current functionality isn't optimal.