I've recently entertained an invitation from a FANG recruiter just to see what they had to offer, and they agreed to skip the screener round and told me "I was already approved for an offer, from HR's end" assuming the second interview round yields good results (this was for staff eng level, if it matters).
My perspective on this: a lot of recruiters and tech leads use automation to find prospective candidates and they tell all of them they found their OSS projects interesting etc, but don't actually understand how that project translates in terms of coding ability on an individual basis (i.e. they haven't actually reviewed code to determine whether e.g. you're actually able to think algorithmically or are just gluing libraries together). That's sort of where the leetcode stuff is supposed to come in: by pushing you through the standardized funnel, they can get a better gauge for how you stack against other candidates. N.B: Whether that provides a good indicator of job performance at all in the first place is a can of worms of its own, IMHO.
My advice: weigh in compensation, career growth and job alignment to decide whether this opportunity is for you. If so, treat the leetcode stuff as a formality: if you have the chops, you should be able to pass with flying colors. The most important question to ask yourself is "what's in it for me?"