The ingress controller with endpointPublishingStrategy of type LoadBalancerService can be created over the following infrastructure at the moment where the external IP gets assigned automatically to the ingress SVC in openshift-ingress namespace through MetalLB.

--> https://docs.openshift.com/container-platform/4.15/networking/metallb/about-metallb.html#nw-metallb-infra-considerations_about-metallb-and-metallb-operator

However, the following annotations for example don't work on the ingress controller to assign a specific IP address from a specific AddressPool to the ingress SVC.

--> metallb.universe.tf/address-pool: first-metallb-addresspool
--> metallb.universe.tf/loadBalancerIPs: 10.13.x.x
 
The above-mentioned annotations can be added to the SVC manually in the openshift-ingress namespace and it works as well but it might not be supported and not feasible in the long term considering that ingress operator pod, SVC re-creation or cluster upgrade might reconcile the SVC and remove those manually added annotations.
 
Many of the customers prefer to use MetalLB for ingress-controller instead of configuring a hardware of software based external LoadBalancer.