Mensa only sets the bottom line, that is, people who must pass the Mensa membership test and prove that they belong to the top 2% of human IQ can join. It is expressed by SD 15, and the Mensa threshold is 130. With SD 24, Mensa threshold is 148.
As for the cleverest IQ, no one knows. But what is certain is that 130(SD 15) is just the bottom line, and there are many members in Mensa who are above 140, above 150 or even higher IQ.
However, it is worth noting that many people who always claim to be around IQ 170 to 190 on the Internet and on TV are expressed by SD24, which is about 145 to 155 when converted into SD 15. Of course, there are still some people who don't know how to calculate it themselves, or even how to get that number, so it is almost meaningless to study that number for most people who don't know the truth.