Generally speaking, Print button does not work, is because of portal printing URL isn't configured correctly.
ERROR when print button clicked
Another example of ERROR when printer button failed, error
should be fixed by use ESRI default printing service URL, old printing URL no longer work
Step 1
Originally portal print URL is like this
https://gis1.victorvilleca.gov/arcgis/rest/services/SecrurePrintService/GPServer/Export%20Web%20Map
This old one does not work any more due to many reason, could be over the years ESRI changed the way it works, or old printing service isn't started or broken. But anyway, I can fix this problem now by using the new default portal printing service URL.
Step 2
Now what is ESRI default print URL
https://enterprise.arcgis.com/en/portal/10.3/administer/windows/configure-the-portal-to-print-maps.htm#:~:text=Once%20the%20PrintingTools%20service%20has,portal%2C%20see%20Configure%20utility%20services.
Correct ESRI print URL will be
https://gis1.victorvilleca.gov/arcgis/rest/services/Utilities/PrintingTools/GPServer/Export%20Web%20Map%20Task
Step 3
Where to set corrected ESRI default print URL
Step 4
Where to fix print button in web appbuilder by paste corrected ESRI print service URL?
Step 5
Test the print button