Adding a large number of songs to a playlist is currently quite cumbersome. I’d really like to see some sort of shortcut to add the song or songs you have selected to the last playlist you added a song or songs to. I’m currently putting together a birthday party playlist and it’s incredibly annoying to do in comparison to cutting edge software like iTunes from 20 years ago.
When you select a song or multiple songs, and click the ellipsis, a shortcut is displayed. Moreover, the pop-up always displays the most recent playlist.
So, it is unclear what you are requesting.