Can't connect to Server.app local sites
Stealth Mode is a feature of the built-in firewall. If enabled, it simply keeps the firewall from responding to ”ICMP echo requests“ (aka Pings). It doesn’t keep browsers from connecting to a web server.

In your case, the reason could be a problem with your DNS configuration. Please check both the client’s and the server’s DNS setup. Try to resolve volhq.mmf.yii.dev from the client’s command line:

host volhq.mmf.yii.dev


and see what reply the command gives you. Get back here if you don’t receive an error…