I discovered that ArcGIS Diagrammer no longer supports ArcGIS Desktop beyond 10.3. This was the go-to tool for reordering fields for a feature class within a file geodatabase. I have subtypes applied, so I have to operate within the geodatabase environment.
Are there any suitable alternatives that would operate with ArcGIS Desktop (specifically ArcCatalog) 10.5 or higher?
While my question is similar to this one and others, most of those fixes are several years out-of-date, and apply to older versions of ArcGIS.