I consider names popular that I actually encounter a lot online or irl. I don’t think you can put a number in it because really, do 50 kids in a million make a difference, do 100, do 10? It’s silly to me to not choose a name because a name is #287 rather than #311 even if the difference is only 20 kids in the entire country, for example.
I’d say top 100. But I also don’t put too much stock into it since name rankings change so much, you could pick a name that’s currently “not popular” and then that name is “really popular” the next year. Like others posters have said, I would pay more attention to my general area since that’s more likely to be a better indicator and more relevant to me.