Given that you are a new user, where in the official documentation have you encountered the term hassio? I am asking because that term was replaced by Home Assistant OS six months ago. If it still exists somewhere in the documentation then it’s a mistake and requires correction.
You may have also noticed that your post was categorized in ‘Home Assistant OS’ (and not hassio). For quick reference, here are the four official ways to install Home Assistant.
There are several existing topics for installing Home Assistant OS on an RPi4 which might help with your intention to use an RPi400. Just search for RPi4. Here’s a recent one: