Hi Eurik123,
Thanks for visiting the Google Nest Community.
A speaker should be a cast enabled device for you to add it to the speaker group. There are Bluetooth speakers that are cast enabled, but if the one you have is a standard Bluetooth speaker, adding it to the speaker group is yet to be supported. For more information, you can check how to Create and manage speaker groups.
We're always looking for ways to improve our product and we'll take it as feedback. I also suggest that you send feedback. Let me know if you have other questions or concerns, otherwise I’ll be locking this thread after 24 hours.
Regards,
Alex
