Although old, everything in this primer for view creation is still current today...
https://yabb.jriver.com/interact/index.php?topic=68960.0These can be quite powerful views to use once created. The attached snip shows a playlist pane I use in my duplicates manager view.
The first three are smartlists. One of those, the one called "All Files", is a simple smartlist using the one rule, [media type]=[Audio] that ensures the unfiltered list always includes all audio files.
The ones that show a checkbox are static playlists. When files are selected in the list, you can tick/untick those check boxes to add/remove files from their respective playlists.
If this is something that might fit your intended workflow, and you need some help setting it up, just shout.
-marko