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I think getting familiar with the format and what they're expecting helps.
Having a human being to interact with during an MMI-style interview will help most people a little as they can see the reaction to their comments and get a sense of when to add more or when to stop rambling on. A human might also ask followup questions in a more natural way which could remind you of more points you wanted to make.
Mainly it is a way to hear how you think things through in novel situations and whether you can react in a reasonable and fair manner.
Schools pretty much have this figured out by now and they will "send" you to a different Zoom Room to interact with each of your various interviewers. You'll get instructions and links on the actual day.
Virtual interviewing took off in 2021 due to the COVID-19 pandemic. This article reviews the platforms being used and tips for applicants.
www.studentdoctor.net
For the OP's question, the MMI and Casper are basically cousins, but performance is not tightly correlated because MMI raters are school-trained to their rubrics, schools choose their scenarios, and live interaction is different than virtual (among other reasons).