You could have a playlist with folders, which you could collapse, expand, nest, etc.

It would then be played in order, yes, recursing through all the layers.

What order did the folders play? Was it usually just the order of the album tracks, or was it more folders of playlists where you custom ordered each? So you might have a playlist of playlists of programming music for instance.

I might be able to replicate this by building a front-end for it which converts it into a flat playlist for Spotify/Apple Music etc.