I have in the past, about 4-5 years ago found some aspects of documentation on MDN in the examples that did not work in browsers because not implemented at the time, as well as some lack of clarity in documenting differences between fit-content function and fit-content keyword therefore I raised an issue https://github.com/mdn/sprints/issues and got the documentation amended. However of course that no longer works for the reasons already mentioned, not sure if there is some other place or process whereby you can raise issues and get documentation changed.
on edit: the issue, 5 years ago https://github.com/mdn/sprints/issues/3723