If you are missleveled as a 6 at FB you’ll be managed out within the year, so you don’t want that. Just be honest, answer the questions you are asked and let the interviewers decide if you would succeed as a 6. Do not try to prepare for what you think we are trying to hear
L6 at fb will be the kind of person tech leading half a dozen engineers day to day
Or someone who has some ridiculous ic contributions where they can show concrete examples of them moving the needle consistently. For example consistently finding ways to increase revenue 1% every year.
I think getting hired at e6 you’ll have to somehow show you can do the first one but describing a similar track record