Have a look at following link:
https://www.postgresql-archive.org/pg-Admin-4-v4-28-Errors-on-launch-td6162407.html
I think this is the fix you need
Hi All
We were not able to reproduce this issue on any of our machines during pre-release
testing for v4.28. Then after some R&D, we are able to reproduce this issue.
Cause of the problem: if value of “HKEY_CLASSES_ROOT.js\Content Type” is set to
“text/plain” then issue is reproducible. In any javascript file, the content type should
be “text/javascript” in the response header but in the above registry setting it is
“text/plain”, so the browser won’t allow it.
Solution: Open the registry and changed the value of “HKEY_CLASSES_ROOT.js\Content
Type” to “text/javascript”.
Update:
PgAdmin4 5.0 is out now, you can check it out here. It seems this problem is no longer an issue. take a look at my screen shot below:
My registry value is still “text/plain” and my PgAdmin works as below shows:
So, if you still have this problem, try upgrade to PgAdmin4 5.0.