The number is well well below 1%. I would bet six figure sums it is below 0.1%.

Effectively nobody has it on. 99%+ of users aren’t even aware of the feature’s existence.

https://daringfireball.net/linked/2023/12/05/icloud-advanced...

You have to remember that there are something like a billion+ iOS users out there. 100 million people have not written down their 27 character alphanumeric account recovery key.