Deezer
As we already know, we have Spotify, Apple Music and Youtube Music in the sidebar player, but we don't have Deezer. One of the biggest music services out there, myself as a Deezer user feel really offended about that.
Imagine that someone wants to listen to their favorite song using Deezer on the sidebar, but just can't because they choose not to place it there, so instead of using the sidebar they just go and open the Deezer website, which is a waste of time and would make the sidebar player obsolete.
Please add Deezer to the sidebar player, just like the other ones.