If you want a book that's more recently, check out Affinity Photo Manual I and Affinity Photo Manual II both published in 2020 and authored by Frank Walters. This book was published in 2017 but is still relevant today because the user interface and tools haven't changed significantly. This book is quite pricey at US $49.99 but it's worth the money for the content, and it's also worth supporting the company Serif who is the publisher of the book simply because they are giving Adobe competition. You can remove those pages and stick them nearby for reference. The last few pages are perforated pages with keyboard shortcuts. They are contributed by Tom Koszyk-founder and creative lead at Hologram Design in Warsaw-and Affinitys own Creative Director Neil Ladkin. Learning by doing is just easier and more enjoyable compared to scrolling through the Affinity help and technical manual. The Affinity Designer Workbook also includes four design projects for readers to follow, teaching brand and logo design, designing for print, UI and apps. You'll learn about the different tools and what they can do. The book is packed with step-by-step tutorials that you can follow along.

This is an excellent book for learning the ins and outs of Affinity Photo in great detail.

Affinity design workbook