I use the app Notability which is available for the Mac and iPad. It combines page-based text editing along with handwriting & drawing support. Typically, I’ll start by typing up my notes for each lesson — and afterwards I’ll add diagrams, lettering, and any other annotation using the Apple Pencil.
For more info about Notability, I recommend this video from Ali Abdaal – who at the time was a Cambridge med school student. He describes how he uses an iPad (and Notability, specifically) to take notes during his courses. This is the video that convinced me to get a new iPad (with Apple Pencil support) and give it a try. I’m glad I did — it truly revolutionized my approach to creating my PDFs & song sheets.
I’ve been making song sheets & musical PDFs for a long time. Here’s a video showing the giant binder of “song notes” I made back in ~2003, a few years after starting to play guitar. Even though the tools I used back then were quite different (e.g. MS Word), it gave me a ton of experience working through the editorial decisions necessary to create easy-to-follow song sheets & PDFs.