I believe I read somewhere that a confidentiality agreement has to be signed

Can confirm.

I wouldn't really worry about the specifics of the scenarios and instead focus on learning the competency and values framework (everything you do on the day is assessed around this) and the Met's vision and values.

Go in with confidence, be conscious of your body language/tone, be mindful of the CVF, stay away from close-ended questions and you'll be okay.

Sorry for not giving a more detailed answer but there's not much else you can do to prepare. Would recommend studying the videos on the page fudgepizza posted just to get a general vague idea.