Nest wifi does not have the capability to block individual websites. It only has a parental control mode meant to block inappropriate websites from children. From my personal experience with Google Home, simply linking your Spotify account to your Google Home account will not give access to it on another user's devices. However if you have Nest speakers and displays in it that use the same account as the one with Spotify linked, then the guests would be able to access your account.
Thanks for lending a hand, @MetalGlacier.
@Casa_Viajeros, you won’t be able to block people connected to your guest network from accessing your Spotify account. Your best option is to unlink your Spotify account from your Google Home app and manually cast instead. That way, your guest won’t be able to access your Spotify account. You can check this article for more details.