This is how to set up a dummy interface on RedHat/CentOS 8.x. I cannot make the old style of init scripts in /etc/sysconfig/network-scripts/ work anymore for the dummy network interface.
Its all NetworkManager now--here is what I pieced together from surfing the web. This one stays up even after reboot:
nmcli connection add type dummy ifname dummy0 con-name dummy0
nmcli con mod dummy0 ipv4.address 192.168.8.88/32
nmcli con mod dummy0 ipv4.method manual autoconnect yes
nmcli con up dummy0
nmcli con show
