If you open Spotify in Chrome (or any Chromium browser), you'll get a little popup, like this: https://i.imgur.com/vw5diI2.png
If you click "Install", you'll get an app-like Spotify icon, it'll show up in applications, you can Cmd+Tab/ Alt+Tab to it with its icon, so on. It's basically an app - but it's running in a separate Chrome window and managed by the browser. Electron but you don't have to install a copy of Chrome every time, basically. (Also, if you're like me and use Brave, this is better in every way.)
If you click "Install", you'll get an app-like Spotify icon, it'll show up in applications, you can Cmd+Tab/ Alt+Tab to it with its icon, so on. It's basically an app - but it's running in a separate Chrome window and managed by the browser. Electron but you don't have to install a copy of Chrome every time, basically. (Also, if you're like me and use Brave, this is better in every way.)