Duplicate of BUG-000176430. This is a known limitation. Indexed and unique GlobalIDs are not supported by the file geodatabase workspace. Refer to https://pro.arcgis.com/en/pro-app/latest/tool-reference/data-management/add-attribute-index.htm#:~:text=Unique%20and%20ascending%20indexes%20are%20not%20supported%20for%20shapefiles%20or%20file%20geodatabases.%20These%20parameters%20are%20ignored%20when%20the%20tool%20is%20run%20on%20a%20shapefile%20or%20on%20file%20geodatabase%20data for more information.