PLSQL-Developer 14: I've build the HTML manual from the Oracle documentation, and the search itself (e.g. for "INSTR") seems to work, I get a list of hits in the Search tab.
However, when I double-click a hit a new tab opens for that hit (which is expected), but the tab seems to be completely blank, no contents is visible.
I assume it's some kind of display problem with the embedded HTML viewer? I have this problem on two computers.

If I right-click in the empty window an select "Properties" I get a property page with an URL like "file:///C:/Oracle/doc/content/arpls/DBMS_LOB.html#GUID-F0F5D13A-C86C-4BC2-8394-8CBA3344D5CE" target="contentwin", so I guess the help has loaded something.

Can you go to Preferences > User Interface / Options and change the "Use Internal HTML viewer" option, restart PL/SQL Developer, and try again?

Thanks for the quick reply! I changed the option and now I see something in the help window.
However, the help does not jump to the topic itself, nor does a click on any of the links seem to work.
See the attached image, I tried to open the help for the INSTR function.
I use the help from Oracle 19.8.

We'll check it out.