https://www.cnet.com/news/reminder-apples-homepod-only-plays-nice-with-apple-devices/

Apple lists the supported audio sources for the HomePod as:

The key here is that, as we discovered during an early listening session, while the HomePod has Bluetooth 5.0 built in, it can't be used for music streaming. You'll need an Apple device that supports AirPlay to remotely play Spotify or other music sources (you also need an Apple device for the initial setup as well). Those other sources also won't have voice control support via the HomePod.