The replacement to Financial Reporting (FR), called Reporting, has been in the Oracle EPM cloud environments for a while now. For the most part, everything I've known in FR has worked about the same. Different navigation or UI, maybe, but all of the same concepts. I'm also glad there are improvements.
With books, one of the common things to do in FR is to set a book POV. So if all of the reports should run for the children of a specific entity, you could simply manage that at the book level. So when I went to Reporting to create a similar book, I tried the same thing. As you might guess, it didn't work. After I got some guidance from Oracle, this blog post shows what it does do, how to do the FR equivalent, and why what to do now is better than FR.
When you create a book in Reporting, there is a book level POV. If you leave it at Default (which means the user's POV) or just select a single member, it works just like the book POV in FR. But if you use a function or select multiple members, like the Entity dimension below, it's different. Instead of running the report(s) for all selected members, it just limits the POV to the selected items. Users view one at a time and do not get a PDF with all of the members.
You can use the options on the flyout menu to control the display but that's about it.
So, what do we do? The key is to use a section. Sections are grouping of reports, other docs, and/or other sections. If you think about an outline, they are the first (or more) top level(s) before you get to the report/doc at the bottom level. They do help with managing the groupings better than FR, which only allowed for collating by member or report. You can see the improved management of it all in a table of contents. Speaking of the table of contents, sections allow for better control over the book layout. Want a cover page before the table of contents? In FR, you couldn't do that unless you had a hardcoded table of contents PDF or Word doc where the page numbers were not dynamic. In Reporting, with sections, it's no problem.
When adding a section, a name field allows for a description to be placed and the dimensions that need a section POV can be selected. These should match what is needed for the report(s).
With the section in place, add the report(s) and then edit the section POV with the desired multiple members. Now when the book runs, the report will run for all of the entities in the section POV, essentially meeting the FR book POV functionality.