Apple Music is a separate part of iCloud from a general iCloud storage subscription.
Click on this link to learn how to optimize the storage actually on the device itself --> "How to check the storage on your iPhone, iPad, and iPod touch" - https://support.apple.com/HT201656 - "If your device is low on storage, iOS automatically optimizes its available space while installing an app, updating iOS, downloading music, recording videos, and more. To make more storage available, iOS can remove some of your items, like streamed music and videos, files in iCloud Drive, and parts of apps that aren't needed. It also removes temporary files and clears the cache on your device. iOS only removes items that can be downloaded again or that aren't needed anymore."