MyBB Community Forums

I know that each forum can be set to its own default sort order at the forum settings
(through forum management section in the forum admin panel)

forum admin panel >> forums & posts >> [click on a forum] >> Edit Forum Settings (tab)
>> scroll down for Default View Options >> Default Sort By "

But where do you change the "Board Default"

the default of the sort order for the entire board itself?

So that it affects search_results_threads and forum display to show newest thread first?

basically latest visible post is shown at the top.
IIRC there is no setting to change the default search order.