TSA; 3x interviews.
Interview 1 (Philosophy): problem sheet - problem solving and logic, discussion based; Interview 2 (Politics): open discussion on questions, two very different interviewers; Interview 3 (Economics): questions on some pre-provided reading, was quite maths-based, but was given more information to help answer questions, felt the most stressful.
Watched videos on what to expect; reviewed subject content; practice interview; practice papers for the TSA.
Prepare in the way that makes you feel most comfortable; voice your opinion but be flexible; don't worry and try not to overthink.
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.
Test taken: Thinking Skills Assessment (TSA)
Number of interviews: 3
Time between interviews: A couple of hours - to a day (one per subject)
Length of interviews: 20min?
Online interview: No
Philosophy: There was a problem sheet: a longer question that I read during the interview(a bit awkward with them watching me read), following into an open discussion, then followed by some short logic questions. There was less time pressure than I thought, and both the interviewers (a professor and a grad student) were quite friendly, they gave me time to ask questions at the end.
I watched some videos about what to expect (especially Chloe Tan's, they were useful). However, it was completely different to what I was told to expect, in that I wasn't asked about my personal statement in any of the interviews. (I know that that's just Merton, not other colleges though). However, I think that it put me in the right frame of mind for interviews, because I felt more confident in my knowledge. I reviewed my IB maths and Economics before my econ interview, which put me in the right frame of mind of "rigorous questioning". I did
I did all the official practice papers for section 1 (10), then reviewed all the questions I had gotten wrong. For Section 2 I wrote some essay plans
I would give advice to do what feel right for you to prepare: for me that meant trying to practice articulating my thoughts concisely, for some people it might be speaking up and not being shy. I think its good to read, but not to name drop research etc, but because it exposes you to different perspectives, and you have more to draw on. You will make mistakes and feel stupid, but just pick yourself up and continue. Don't be afraid to argue a point, if you have an opinion voice it, but equally, be flexible enough to change course when/if they convince you otherwise. Also, I think its impossible not to overanalyse afterward.