It’s not region locked, and as the sibling post notes it’s been there for a while. I’m not sure how much more simple it can be made (open Settings, tap Apps, and there it is at the top of the page).

I suppose it could be possible for apps to prompt the user to change the default, but I’m honestly pretty sick of that behavior on desktop (e.g. I have several browsers installed for various reasons and they nearly all bug me about being default) and would rather not see it copied to mobile OSes too (I don’t believe Android allows apps to show such a prompt either).