Ok, so I'm almost there. Yes, I had changed to Access Point since that seemed natural to me, but that option only allows for wired connection. So I went back to Router and I followed all the steps....

I got the Archer C7 - AC1750 and I wanted to use it as a wifi repeater. Before buying it, I saw this thread and it seemed possible. https://community.tp-link.com/en/home/forum/topic/254836 However,...