There’s probably hundreds of references in your bibliography. There are possibly dozens of papers written by your examiners. Many pages in your thesis. There are several books on viva preparation. There are thousands of posts and articles about the viva (almost a thousand on this site alone!).
Is everything must read? Do you have to read everything in order to get ready for the viva?
Of course not, but you have to find the balance right for you.
You need to read your thesis. You need to be familiar with your literature and what your examiners’ interests are. And it will help you feel confident knowing that your prep follows good ideas and principles. You have to see where the gaps are for you, and find good sources to bridge them.
It’s not all must read.