What I'm most interested is not usage of "gotten", but whether somewhere in the English-speaking world, using "I've" standalone (without a follow-on got, been, had etc) is normal.

I see it from time to time online, and immediately assume they're a non-native speaker who doesn't understand the nonsensical nuances of the language.

Eg people will say something like "I've 3 apples", which is just "I have 3 apples", which is perfectly gramattical. But, for some reason, we use "I've got 3 apples". But I think we'd also say "I have 3 apples" and not "I have got 3 apples".

Language is weird.