In previous OSP releases, the recommended configuration is to configure either Controller and/or Networker nodes as OVN gateways. See [1]:

In OSP18, currently VA1 doesn't configure any node as GW. In this case, OVN schedules the  gateways on compute nodes as they are the only nodes with ovn-bridge-mappings set. Using computes as GW nodes was not recommended in previous releases, according to [1].

According to ykarel@redhat.com 's research (see [2]), configuring OCP workers where control plane pods run as GW nodes is possible. The architecture repo needs to be updated for this.

[1] https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/17.1/html-single/configuring_red_hat_openstack_platform_networking/index#create-custom-network-role-ovn_work-ovn

 [2] https://issues.redhat.com/browse/OSPRH-3240