The documentation [1] for configuring a local ariber with 2 control planes still suggest to add the field `featureSet: TechPreviewNoUpgrade` in install config. 

[1] https://docs.redhat.com/en/documentation/openshift_container_platform/4.20/html/installing_on_bare_metal/installer-provisioned-infrastructure#ipi-install-config-local-arbiter-node_ipi-install-installation-workflow

Since the feature is no GA, the sample install config should not have the field `featureSet: TechPreviewNoUpgrade`. 

The cluster does start installing when the field `featureSet: TechPreviewNoUpgrade` is removed from install config file.  

Follow the document [1] and try installing a 2 node cluster with a local arbiter. Removing `TechPreviewNoUpgrade` does detect the local arbiter and installation starts.

[1] https://docs.redhat.com/en/documentation/openshift_container_platform/4.20/html/installing_on_bare_metal/installer-provisioned-infrastructure#ipi-install-config-local-arbiter-node_ipi-install-installation-workflow

    1. Follow the document - https://docs.redhat.com/en/documentation/openshift_container_platform/4.20/html/installing_on_bare_metal/installer-provisioned-infrastructure#ipi-install-config-local-arbiter-node_ipi-install-installation-workflow     
    2. Remove the field `featureSet: TechPreviewNoUpgrade` as suggested in sample install config file.
    3. Install the cluster.
    

The documentation suggests to add `featureSet: TechPreviewNoUpgrade`

Since the feature is no GA, the field should be removed from sample install config.