90-9-1 principal is considered the truth, though I've not seen any rigorous studies to back that up.

https://www.reddit.com/r/TheoryOfReddit/comments/s2dvr4/the_...

https://en.wikipedia.org/wiki/1%25_rule_(Internet_culture)

At the very least I'm confident it's a power-law distribution. 90-9-1 seems like a reasonable first-order estimate (but I've also seen no data)

I think it’s single digit percentages that have an account.