I have a field in the Attribute Table for a Feature Class [FC] that contains a UNC value that points to a word processed file. The field is called WriteUp and is a text field with a length of 100.
Taking instruction from this ESRI web page I entered the UNC for the word processed file into that field. The UNC points to a locally networked NAS box.
To make sure that I had permission to access this I entered the UNC into Windows File Explorer and was able to properly access the file.
In the ArcGIS Pro pane Configure Pop-ups for this FC I entered a Text element, edited that element using the Hyperlink dialog and entered {WriteUp}, where WriteUp is the name of the field that I want to access in the Attribute Table.
On opening the Pop-up the hyperlinked text field displayed the correct UNC but was unable to open the link by clicking on it. When mousing-over the field, the absence of the hand cursor seems to indicate that the link is not available.
I have another field in the same Attribute Table called Content which contains a URL for a web site. I built its Pop-up text entry in exactly the same way as the WriteUp Pop-up entry. This works just fine.
Here's a screen shot of the Pop-up.

Clues would be very welcome. Thank you.