Where are you getting your information?
Six months ago, hass.io was officially renamed to Home Assistant OS.
The official documentation doesn’t contain any reference to the deprecated name so whatever you are using as your reference is at least a half-year out of date.
There are four ways to install Home Assistant and the table in this post can help you to understand the differences:
Basically, your intention to use Home Assistant Core, instead of Home Assistant OS, means you will forego the convenience of the Supervisor which, among other things, includes Add-Ons.