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Japan to crack down on Apple and Google app store monopolies
(asia.nikkei.com)
This is a most excellent place for technology news and articles.
Honestly, I feel like they've made side loading easier and easier as times go on. Used to be that you'd just get a pop up that installs weren't authorized for that app, then you had to dig through the settings to enable it. Nowadays the pop up has a shortcut to the correct settings page and even visually flashes the right toggle for you to make it easier to find.
I could be wrong but I think at one point the outside sources toggle was just a one time thing and affected all applications.
You're right, it did use to be that way and I'm pretty sure it also automatically took you to that particular setting when you needed it