The Book of Life
Most translations of Revelation will say there’s something called the ‘Book of Life’, even capitalizing the words to make it appear as a proper noun.
However, the text does not call it that, it just says that ‘another scroll’ (or book) was opened, and it’s the one ‘of life’. This probably means that it’s the scroll that’s about life, or regarding life.
It’s likely referring to Psalm 69:28, which mentions unfaithful ones having their names removed from the ‘the scroll of life’, echoing what was first recorded at Exodus 32:33 where God says he’ll do that.
In other words, it’s a description of the book, a reference to the book that God and David both mentioned. Yes, strictly speaking, it’s not the book’s title. That’s why our translation says:
‘Then another scroll was opened, which is the [one] of life…’
Calling it ‘The Book of Life’, with capitalization, is just a tradition.