internet sharing from a wifi-connected mac over ethernet to create second wifi network

I live in a building where our landlord functions as an ISP, which charges above-market rates for internet access. Therefore, I purchase internet from Xfinity instead, via a wifi hotspot. I access the internet through a Mac Mini, which is registered with Xfinity’s wifi network. There are many answered questions about sharing internet between a Mac and a second device. But I could not find an answer to how to share internet between a Mac and many devices, using a wireless router connected to the Mac. It is similar to this question , but using a Mac. I tried connecting the Mac’s ethernet port to

Question by Dianna on Super User, licensed CC BY-SA. We show a short excerpt and link to the original thread as credit.