(request) You can make stadia app on Mac OS the same as YouTube Music app to open as a separate app.
Do you mean that Chrome just open a "non webbrowser"-ish new app window?
If yes, you are able to to it by your own. I hope this article helps: https://www.webnots.com/how-to-create-desktop-shortcut-of-a-site-from-google-chrome/
YouTube Music opens on mac os as a standalone app and stadia as a chrome site.