Thanks for reaching out.
According to my personal experience and the feedback I had from other interviewers in MBB/non MBB, the difference between interviewer and interviewee led is as follows:
In an interviewee-led case, you will have to get the lead (ask the right question, go deeper in your analysis and make an hypothesis and test it).
An interviewer-led (McKinsey style) case will be more guided with questions during the case. The interviewer will first give you the case context and the ask you to tackle the main drivers for the case. After that, they will try to dive deep in some parts of your structure.
This said, you have to ba wary of interviewer led cases. They are usually giving you extra points if you take the lead in this kind of cases.
However, when you are interacting with more senior interviewers (for example last round of McKinsey, where you will be interacting with (senior) partners, the case will be less structures and they will appreciate the fact that you took the lead and went through your structure while asking the right questions and testing your hypothesis.
All in all, those two concepts are not very clear for interviewers usually, and I advise you to prepare both if you are applying for McKinsey and to focus more on interviewee-led cases if not.
Best of luck for your interviewe, and do not hesistate to reach out to me if you need any help/further advice.