Exceptional
There are viva regulations for your institution, general experiences from the massive number of vivas that happen every year and the particular practices of your department. Together, these combine to give a picture of what to expect at the viva. You can have a good sense of what a viva is supposed to be like by taking all of these into account.
There are always exceptions.
Most vivas have two examiners – apart from the ones that have three. Most examiners are academics at other universities – apart from the ones that aren’t. Most vivas up to 2020 were in-person – apart from the ones that weren’t, and then apart from all the ones that suddenly weren’t!
Your viva might be exceptional too. You might have done something a little different in your research or created outputs that most PhD candidates would not. Your thesis might be different. Your viva day might start differently. You could have requirements that many candidates never think about.
Exceptions change the viva but don’t change the purpose. Exceptions might shape your viva but they don’t alter the overall process.
Vivas are always unique and the exceptional people who have them are uniquely positioned to succeed whatever the circumstances.