I found an official guide when hunting around in the Minecraft Help Center, but it also seems to not work just like the unofficial one I mentioned. It says to go to the 15th anniversary page (the one that currently tells us about buying tickets for Minecraft Experience) and scroll down to the “Get the 15th Anniversary Cape!” section, which doesn’t seem to exist anymore. So I think this is just a case of Mojang not updating their help page’s information. I decided that as much as I really want the cape, I can’t be bothered going through Microsoft Support for it; Microsoft Support just sucks, lol.
Because the general population doesn’t know much about data privacy and they are purposefully mislead and inticed into accepting agreements that share all that information out. The point of NBTV is to raise awareness.