This has been working for me for a while, though it seems lots of people get different html so it may not work for you:

  facebook.com##div[data-pagelet*="FeedUnit"]:has(div[aria-label="Sponsored"])
  facebook.com##div[data-pagelet*="FeedUnit"]:has(span[aria-label="Sponsored"])
  facebook.com##div[data-pagelet*="FeedUnit"]:has(a[aria-label="Sponsored"])
  facebook.com##div[data-pagelet*="FeedUnit"]:has-text(Suggested for You)