The search box at the top right of most forum pages has some significant limitations. I rarely use it. Note that it does not allow searches of words of 3 characters of less, so one cannot search for AFB, EFB, AHB, DNA etc.

What I do use is Google Search, or DuckDuckGo Search, but with the "" keyword that limits the search results to just Beesource. For example, a search for the term "drone DCA" in a Google/DuckDuckGo search box would look like this:
drone dca

That works well, allows searches for terms of 3 characters of less, and also allow you to use other Google "tools" as well (ordering/limiting by date etc). Also, clicking the "Images" tab in the results allows you to see photos posted to threads that are returned by your search.

If you want to search for posts involving a specific Beesource member, use the forum Advanced Search, instead:
The link is to the "Search Single Content Type" and works better than the Multiple Content tab. But this search feature has no advantage if you are not looking for a posts by a specific member, and the Google search is a better choice in that case.

Also, the specific value of advanced search results returned are greatly affected by the "Show Results as Posts" button in the "Additional Options" box near the bottom of the page. The default is "Threads", not "Posts", but "Posts" are more useful when looking for results from a specific member.

It is possible to get the options set for the way that works best for you 'most of the time', then Save that set of options for future use. "Save" is at the bottom left.