This is minor, but on the first page of Chapter 3, "Generics and Collections", it currently says:
When studying for the 1Z0-815 exam, you should have studied other functional interfaces like Consumer, Function and Supplier.
In the first book of the two book Java 11 Sybex books, and presumably the corresponding earlier chapter of the CSG, the functional interfaces introduced are Predicate, Comparator, Consumer and Supplier. The first book (or earlier chapters of the CSG) never makes use of Function<> yet.
If Oracle maintains the unified "one big test" approach for the future, you may have some re-org anyway around the earlier, now artificial, split of topics between the 815 and 816.
Both chapters 3 and 4 of the 816 book are pretty thick/fat/hard as it is, but chapter 3 was my first J & S (B & S?) led introduction to Function, just to note.