As i have set up a windows 2019 trial server for testing some stuff some days ago, i configured the virtual machine (under virtual box) as a domain controller.
So i configured the role for DNS and AD services as i got the window for prerequisites check. it failed!
The error „Verification of prerequisites for Domain Controller promotion failed. The TCP/IP networking protocol must be properly configured. Complete the configuration before you proceed.“
Sounds dramatically bad! But keep up that your virtual network card is connected to a virtual switch or is bridged to your host. And keep up further that you set up a fix ip adress with subnet and routing target and and dns server.
So that worked for me.