2x interview (20 mins each), 1x test (1 hour, with 30 min prep)
General controversial topics discussed.
Read the news, think of topics you're interested in.
Don't overthink - they don't expect perfect or right answers, talk them through your reasoning.
Remember this advice isn't official. There is no guarantee it will reflect your experience because university applications can change between years. Check the official Cambridge and Oxford websites for more accurate information on this year's application format and the required tests.
Also, someone else's experience may not reflect your own. Most interviews are more like conversations than tests and like, any conversation, they are quite interactive.
I had two 20 minute interviews. The first interview kicked off with my personal statement. I was then given a problem and 30 minutes to prepare for it to be discussed in the second interview. There was also a one 1 hour test where I had to write an essay on a given title.
We discussed general controversial topics (you can bring in topics but be careful not to steer the conversation in a way where you are not answering the questions asked). They just want to know how you think.
Read the news! Have controversial issues in mind that interest you. Practice being able to see and explain both sides of an argument.
Don't overthink what happened in the interview. Make sure to talk the interviewer through your thoughts. They are asking difficult questions and they do not expect you to have the perfect answer to everything.
Ultimately, they want to see how you can reason through difficult issues and the best way to do that is take them through your reasoning - this will also give them something to work off of and generate a real discussion.