Hey ShackieChan
We understand you're seeing over 5GB of storage being used for Apple Music. Whenever your iPhone needs to make more storage, it will remove items such as streamed music and videos. It will also clear the cache from your device and remove temporary files. There isn't a manual way to remove cache files.
Do you see any songs listed in Settings > General > iPhone Storage > Apple Music? If so, delete them and see if it frees up space. If you continue to experience the issue, delete the Music App and then reinstall it: Delete built-in Apple apps from the Home screen on your iOS 14 or iPadOS device or Apple Watch.
Hope this helps. Take care.