Music from Apple One not in iCloud

• Do you have Sync Library turned on?

Use Sync Library with your Apple Music subscription - Apple Support

• Are you a member of a family plan and not the Organizer?

• Do you see iCloud storage being used when viewing at Settings > [name on top] > iCloud > Manage Account Storage?

Did you recently transfer from an Individual Apple Music plan to Apple One?

Not sure if the music you are referring to was when you used the service previously using a subscription and now wanting to access it again with Apple One or something else.