Google will not be bringing YouTube Music or its updated Google Maps app to Wear OS 2 smartwatches. Instead, older Wear OS devices will receive overhauled Google Pay and Messages apps. Thankfully, Spotify has come through with offline playlist support for Wear OS 2 smartwatches.
https://www.notebookcheck.net/No-YouTube-Music-Google-confirms-the-state-of-new-apps-and-services-coming-to-older-Wear-OS-2-smartwatches.555075.0.html