ArcGIS Pro 2.5 will not allow me to "Configure Layer for Locate" in the Locate window if the layer has a join on it. Is that on purpose or is there something else I need to change to allow that layer to be used?
The behavior you are experiencing is a known issue, BUG-000114925 that I have found to work under certain circumstances.
Have you tried your join scenario using the Layer Search tab of the Locate pane to search in all fields of the layers in the map? Are you using the configured layer workflow outside of ArcGIS Pro?
Retrieving data ...