It’s actually linked in the top post of Set up Reply via Email Support:
Alternately, if you aren’t comfortable using GMail for this, you can set up your own incoming email service using Straightforward direct-delivery incoming mail
Your original post doesn’t specify which documentation you were following to go down the POP3 rabbit hole, but assuming you were looking at the official guide linked above it has been linked in there since March 28.
I’ve responded to your reply in the other topic to suggest how to structure addresses/domains when using this.