Ingress capability was introduced in 4.16 and always needs to be enabled in standalone OCP.

We requested doc update in https://issues.redhat.com/browse/OSDOCS-10806, but related section in 4.16+ RN and doc[1] are removed via https://issues.redhat.com/browse/OCPBUGS-41971 recently.

FYI, installer also has such pre-check to make sure that ingress is always enabled.
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$ ./openshift-install create manifests --dir ipi
ERROR failed to fetch Master Machines: failed to load asset "Install Config": failed to create install config: invalid "install-config.yaml" file: capabilities: Invalid value: types.Capabilities{BaselineCapabilitySet:"v4.15", AdditionalEnabledCapabilities:[]v1.ClusterVersionCapability{"CloudControllerManager"}}: the Ingress capability is required 

Suggest to add them back and do some minor changes based on the description of bug OCPBUGS-41971.  

[1] https://docs.openshift.com/container-platform/4.16/installing/overview/cluster-capabilities.html     

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