Internet mac mini not working

1. 1. On your Mac, choose Apple menu  > System Settings, then click Network  in the sidebar. (You may need to scroll down.)
2. 
   
3. Click the Action pop-up menu  on the right, then choose Set Service Order.
4. Drag services into the order you want.
5. Click OK.

The interface that connects to the Internet should be dragged to the top of the list.

System Settings>Network>choose interface>Advanced>Proxies Tab, make sure none are set, like for HTTP & HTTPS.

If using Wifi, instead of joining your Network from the list, click the WiFi icon at the top, and click Other network>Other. Fill in everything as needed.

System Setttings>Network, click a network service on the right, click Details, then click DNS. (You may need to scroll down.)

Enter these numbers...

8.8.8.8

8.8.4.4

1.1.1.1

9.9.9.9

Did rebooting the router and the Mac fix it?

My router (actually a gateway that combines the features of both modems & routers in one device) firmware obviously recently had an issue where it after a few months failed to give DHCP IP number to a client and rebooting fixed that (or just lightly fiddling with the router with a device that still could connect to it).

I believe the latest gateway FW update should fix it but I have not yet applied it because the current updated FW has worked OK for a few months.