IMO there's too much of a difference between 2.9 and the 5.x versions. When 5.0 came out, they made major changes. It wasn't just an update.
There is a new book out specifically for 5.x. Draw and Paint Better with Krita by Wesley Gardner. I watch his YouTube videos. He's very knowledgeable and a good teacher.
https://www.amazon.com/Draw-Paint-Better-Krita-illustrations-ebook/dp/B09YHRCSKB