When selecting a feature in ArcGIS Field Maps, the value is displayed from the Display field if the field set for the pop-up title has a null value.

Workaround

Refer to the worflow from the article, but use the following expression: IIF(isEmpty($feature.name), "No title", $feature.name)

Note: If the text is not specified (such as "No title") but uses " " instead, the title defaults to the Display field.

Steps to Reproduce