Greetings isadavtho,
Being able to add music to your library using Siri on your HomePod is a great feature. To confirm, was the HomePod set up using your Apple ID or a family members Apple ID? Have you confirmed that you have access to Apple Music on your other devices? If you don't have access to Apple Music on your other devices, you'll want to have the family organizer share the subscription with you. They can confirm that Apple Music is shared with by going in to Settings [their name] > Family Sharing, they should be able to see Apple Music, along with the list of family members the subscription is shared with. They may have to tap on the subscription to see a full list.
Let us know how that goes!