I'm not sure if you actually read most of what I said or are just responding to the part where I said it was easy, but, at least on android 9, it automatically

I'm not sure if you actually read most of what I said or are just responding to the part where I said it was easy, but, at least on android 9, it automatically takes you to the setting as soon as you try to open an apk, acquiring which, is pretty much exactly the same as downloading an .exe file on a computer. Depending on your browser, it will even ask if you want to open the file upon completion, thereby taking you to the 'enable apps from unknown sources' option without even leaving your web browser. I like to have faith that most people capable of downloading and opening a file from the internet, should be able to read a message pop up and tap a toggle button.