There is a strange behavior with the new version 4.28 that is addressed in the FAQ:
When I launch pgAdmin 4 v4.28 or later on Windows, the loading page
never closes. Why?
pgAdmin 4 v4.28 includes additional security features, one of which is
intended to prevent security issues caused by Content Sniffing.
Unfortunately some Windows systems are mis-configured such that this
causes Javascripts used by pgAdmin to fail to load. Opening the
developer tools on your browser will show an error similar to this:
Refused to execute script from
'http://127.0.0.1:57313/static/vendor/require/require.min.js?ver=42800'
because its MIME type ('text/plain') is not executable, and strict
MIME type checking is enabled.
(index):39 Uncaught ReferenceError: require is not defined at
(index):39
This will occur when the value of the registry key at
HKEY_CLASSES_ROOT\.js\Content Type is set to text/plain. To resolve
the issue, use the Registry Editor and reset the value of
HKEY_CLASSES_ROOT\.js\Content Type to:
text/javascript
Finally, restart the pgAdmin server.