unable to ping local network
Ping can be suppressed by a firewall, so I like to take a more overall view.


I would choose one thing that Macs can share like Screen Sharing and File Sharing and turn them on on both Macs.
I would check if the time of day is correct on both (since some deviation past a few hundred seconds can cause visibility errors in some sharing tasks). This also ensures that the network connection to internet time servers is working if you set the time automatically.
Now that you know the network itself is functional for each Mac - open Finder in both and search for the other Mac.


If you have hidden the "shared" sidebar in finder, you might have to un-hide it. Alternatively, you could make a new test user account on both Macs and use it for troubleshooting. The default Finder settings will show shared Macs on the local network.

At that point, you'll know a bit more about the network and possibly want to power off both Macs and power off the router and then start them all up again.