That I can close Spotifty's window, and it keeps playing in the background in Linux Mint, is one of those details of using a computer that makes it a lot better that you don't miss until you can't do it.
Currently I'm using Linux Mint 21.3 Virginia, but I was able to do so since Linux Mint 21.2 Victoria. And I'm using Linux Mint's system packages, not the Flatpak version of Spotify Linux client. Not that I dislike the Flatpak version of app, just that I prefer using system packages of the apps I trust.
For some years, if you wanted to keep Spotify running on the background on Linux, you had to use workarounds to be able to do so. Not the optimal thing to do, specially for people who didn't know how to do so or wanted to have do some extra steps to be able to do so. So much so, that I got tired of it and stopped doing it
Yet, being able to do so out of the box is something that I really enjoy. Specially since it is something you can do on other OSes like Windows. And to be honest, is one of those small things people notice on an app behavior when they make the jump to Linux from an OS that supported being able to run Spotify on the background when you closed the app window.
For me, that I can run Spotify on the background, just like I do with Rhythmbox, is one of those things that makes the whole user experience of using Linux Mint a lot better. Specially because Spotify has become an integral part of how I consume music and podcasts on daily basis.
Spotify helps be discover new music, and listen artists and songs I already loved wherever I am. Also listen to the podcasts I love on the move, no matter where I am at the moment.
Which is great for me, since I like to so while commuting or walking.
Spotify has become my go to music and podcast streaming service, and it restored functionality of running it on the background when closing the window on Linux Mint has solidified its position for me.