Not all my music transferred to my new ipad

Most, but not all, data can be directly copied to a new device.

Any Music/Media content, transferred from your PC/Mac using iTunes (or Finder on later Mac computers) - or “Paid” material downloaded from Apples iTunes Service - must again be downloaded to your iPad.

The reason for this intentional limitation, deliberately imposed by Apple, is to protect Copyright. In the case of iPadOS/iOS, Digital Rights Management (DRM) prevents direct copying of copyright material between devices is inhibited. This is intended to prevent the creation of illegal copies of potentially copyright material.

The iTunes Application on your PC/Mac maintains an authorised copy your media - whether this material is loaded from a CD, or downloaded from the Apple iTunes Service - and media derived from this library can be transferred to your iThings.

I hope this information is helpful to you in resolving the issue.