So on the desktop client, you can click and drag a track from pretty much anywhere to your play queue.
Now Playing window in the bottom left? Go for it!
Another playlist? Sure fam.
Albums? Artist pages? No sweat.
Your Library? Daily Mixes? Of course!
Radio? Why not?
Play Queue? Nah dude can't do it. The mouse cursor just turns into a little sign for 'no'
Personally, I think it was just an oversight and should be an easy fix... right?
Updated on 2019-03-18
Your idea was submitted a while ago and unfortunately didn't receive the amount of kudos needed to stay active in the ideas board (100 Kudos per year).
In order to keep the Ideas Exchange clearer I'll close this idea for now, but this doesn't mean Spotify rejected this idea.
If you think this is an idea which needs to be implemented, you're welcome to post it in slightly different again 🙂
Have a nice day!