How to copy Music library from Mac on to iPad

iPods started out with the model that you had a computer that held the master copy of your music library, and that to load music onto your iPod, you did one-way synchronizations, from your computer to a hidden music library on your iPod. No directly accessing iPod music files, or uploading them to another computer.

That model has persisted – with modifications. You can now buy music from the iTunes Store directly on the mobile device itself. You can take out an Apple Music subscription. The Music app serves double-duty as an app that lets you play music from your library, and as an app that lets you play music from your Apple Music subscription.

So to get music from your own CDs onto your iPad, you first need to import the music into your Mac's iTunes/Music library. Then you need to synchronize the iPad with the Mac or PC.

Sync music between your Mac and iPhone, iPad, or iPod touch - Apple Support

In pre-Catalina versions of macOS, you used iTunes to do this. Starting in Catalina, Apple split iTunes into pieces, so you'd use the Mac's Music app to build and manage your Mac's music library, and the Finder to load selected music onto your iPad (using the synchronization interface, rather than direct access to the iPad's music library).

What happened to iTunes? - Apple Support