This worked for me in a new install of v12 - specifically adding the sitename (ex site1.local) in /etc/hosts on the ERPNext server and calling that sitename from the browser (ie http://site1.local:8000)
here’s what the entry in hosts looks like on the server
127.0.0.1 site1.local
here’s what the hosts file entry looks like on the client (browser side)
192.168.0.223 site1.local