3 billion seems like decent number to use for how many Android users there are [1]. 4.5% of 3 billion is 135 million or about 13x more than Google Domains [2] so I guess not major indeed.

[1]: https://www.google.com/search?q=number+of+android+users

[2]: https://www.theverge.com/2023/6/16/23763340/google-domains-s...

I wonder how skewed to poorer countries that is? Also I imagine some skew towards smart tvs (since they outlive older phones, you could easily have a 2013 smart tv still working, I had a 2009 dumb TV until recently and sold it on).

6.1%, those using 7.0 and older will be affected. But that number will have fallen a bit by the time the certs actually expire in a year.