My understanding, based on a related comment in this thread, was that premium accounts get higher quality; in that case, I figured any such checks would be server-side.

If you were referring to a separate check in the above repo's code, my mistake.

Hm, maybe. I don't remember whether they offer higher quality. If they do, it would make sense to have that check on the server side. It's been a while since I last used Spotify because they deleted my account in 2022 without warning when they left Russia.

But I was referring specifically to all third-party reverse-engineered Spotify players requiring premium accounts to function at all.