Personally, the following topics are of interest to me:
- Namespaces practical use in CI4 with examples
- Routing and more practical examples
- Working with database - real app with examples queries
- How to use .env in practical examples
- How to use Filters in practical examples
- How to use Events in practical examples
- How to use Honeypot in practical examples
- How to use Migrations in practical examples
- How to use and work Cache / DB-cache in practical examples
- How to create API in practical examples
And ofcourse i am very waiting your book
https://leanpub.com/codeigniter4foundations