In Redhat 8, every time you the Network Manager get’s restarted it overwrites /etc/resolv.conf. To prevent that from hapenning, create a new file called /etc/NetworkManager/conf.d/90-dns-none.conf and add the following lines. Restart Network Manager. Your /etc/resolv.conf should be unchanged.
[main]
dns=none
Restart Network Manager
$ systemctl reload NetworkManager