You're a member of a large Facebook group in which thousands of members can post and comment without approval. Non-members cannot post without approval. How can you indefinitely limit the number of posts (and, ideally, comments) of members to at most one every time unit, e.g., every week? (A week, i.e., 7 days, is only an exemplary value that would probably fit you best — every day or every month could hypothetically also do, and you might wish to adjust this value later.)
Background: Your group receives too much attention, and so far you couldn't find any co-admin or moderator who would do proper daily cleanup of posts and members. You don't wish to turn on the approval for everyone since otherwise you'd get a list of tons of stuff to approve. You also do not wish to pause (or archive or otherwise turn off) the group. You wish only to limit such activity forever (so that you don't have to bother about it again) and generally, i.e., for all the thousands of the members.