The Pen Tool is the heart of Illustrator. A good PDF will teach:
Users gained the ability to embed Photoshop cloud documents directly into Illustrator and revert to earlier versions of saved cloud files. Adobe Illustrator 2021 Tutorial Pdf
Tutorials Point offers an "Adobe Illustrator CC" PDF that directly aligns with the 2021 interface. It’s structured with bullet points and code-like shortcuts. The Pen Tool is the heart of Illustrator
The Feature Summary (October 2021 release) details several key advancements that improved designer workflows: Adobe Illustrator 2021 Tutorial Pdf