That's why longevity matters.
Yes, exactly.
How many people in the world have never - ever - had anything to do with social media (which is a very new phenomenon, relatively speaking)?
(I don't have the answer - I don't think anyone does, and it will be just an estimate, but I think even the estimate would be shocking to some.)
How many of
those people (who have never - ever - had anything to do with social media) would recognize the name of - say - "Donald Trump", "Joe Biden" or - yes, why not - "Michael Jackson"?
That's where you should
start - and then look further into how likely it is that
those people would recognize "Cristiano Ronaldo" over "Donald Trump" (or "Michael Jackson", for that matter). And
then - yes, of course - you can also look into how many of the non-social media demographic would actually recognize Ronaldo (many of them undoubtedly would).
Anyway, the point is that how many followers Ronaldo has on Instagram is an extremely doubtful indicator if what we want to establish is how objectively "known" he is (that is, how many individuals on this planet are able to identify him by name or image).
My guess would be that he is - by reasonable/relevant/mostly accepted standards - very well known. But I would be surprised if he's
more known - across the globe - than even someone like Joe Biden.