In this video, Terry White shows how to use your iPad or iPad Pro with Apple Pencil as a graphics tablet on your Mac. The feature is called Sidecar and works with Mac OS Catalina 10.15.x. You'll want an iPad and Apple Pencil as well as a Mac running Catalina to make this work.

Here are the Sidecar requirements: https://support.apple.com/en-us/HT210380