From PTC Windchill, when you try to link a change request or a part to a CCM work item or RM requirement, the selection dialog may not be showned. The result depends on the browser:
Blocked by Content Security Policy
When this error happens, you've to add the Windchill server to the CLM URLs whitelist. Here is how to proceed:
Add New Whitelist URL section.
Check you don't face the issue anymore and you see the delegated UI instead.