Extend WiFi to a LAN via computer as router

Basically I would like to log into an xfinitiwifi hot spot access point with appropriate account credentials on an old PC and then, using the PC route that signal to a LAN. From a network card in the computer, I would like to connect more than one device acting as wireless access points (router, WAP, etc.), ideally in a mesh. I expect that this can be done but have no idea where to start. The solution does not necessarily need to be via OpenWRT, but this seems like a good place to start. Presently, I'm using this (https://www.amazon.com/dp/B0BF9KM4MZ) as a repeater/extender for that purpose, but need to operate a LAN on the local side of the repeater/extender. It seems like a good opportunity to explore what I can do with an old computer...Where do I start with such an project?

The Ethernet jack on the side of the unit you have is supposed to do that. If you need more than one LAN device, add a switch.