Spotify or MacOS leaking information between users?

I have a Macbook M1 running MacOS 11.6. I'm logged in to MacOS with an Admin account. I have Spotify open. I'm logged in to Spotify. Another MacOS user with a Standard account logs in to MacOS. (The Admin account was never logged out of MacOS, just switched accounts.) The Standard account user never sets up anything or logs in to anything using Admin account's credentials, of any kind (it's a different person with their own accounts). The Standard account is not logged in to Spotify. I go to listen to Spotify on a different Macbook, using the same Spotify account. There's a "Now Playing" icon in the menu bar of the Standard account on the original Macbook. They can see what I'm listening to and pause my music. How is that possible?

Solution 1:

Apps installed in the regular Applications folder are accessible to all users. I think it may be a limitation of Spotify itself that it doesn't recognise if a different user is front-most, but there's a workaround.

Switch back into your account on the affected Mac [you may need to log all other users out before you can do this, haven't tested]

Quit Spotify.
Open your Applications folder & scroll to the Spotify app.
Then open /Users/[yourname]/Applications

Drag Spotify from one to the other, whilst holding Cmd ⌘ [otherwise it will make an alias.]

Relaunch Spotify.

The app should now only be available to you.

I don't see a 'now playing' item in the menu bar [I'm on Mojave] so I can't test for that, but the app should now be unavailable to any other user.
Further investigation finds there are several 3rd party apps to add the menu icon, Spotify itself doesn't have one [unless it was added for the M1 build, which I can't test]
That may make the above workaround invalid. Instead you may have to do the same to the menu bar app.