I'm probably naive, but how the heck does one search the forum by keyword? I can't see an entry-field anywhere

I would recommend you to use "site:forum.dji.com <search term>" on Google.

Thank you. I have now saved that as a Favourite Page & then will simply replace "search term"  with  particular words relating to my search.
However,  it would be far better if DJI included a proper google search engine within the forum, but then, I see so many pleas for improvements  in Software that I know you must be awfully busy with those....