It’s reasonable to expect your examiners to ask you to summarise what you’ve done. It’s a fairly common opening question. Given that a thesis could run to many tens of thousands of words it’s probable your examiners would want you to be concise in exploring or explaining what you did.
Being asked to give an overview, either of your thesis, your research or your results, shouldn’t be too taxing for you. Over the course of your PhD you will have spoken about your work many times and given “the short version”. You will have written about your research in lots of ways. There’s lots of practice and material in your mind to draw on when you get to the viva.
A little more rehearsal won’t hurt you though!
In the weeks leading up to your viva consider what you would typically say if asked to summarise your work. Perhaps write it out or record yourself and reflect: Does this really capture it all? If there was one thing to add, what would it be? Find a good opportunity to run it past your supervisor or a trusted friend and get their opinion.
If asked to give an overview or summary in the viva, there’s no way you can tell your examiners everything that might be possibly relevant. A little rehearsal before the viva can help you be sure that you’re giving them enough.