I did what I thought you described, and it found posts in several threads in several forums. I am using a browser. Maybe I wasn't limited to the current forum.
I never saw the popup you showed.
I used the menu bar option "Search forums". That took me to a search page. "Search threads" under that found posts in different threads in different forums. "Search forums" found things, but didn't have the option of displaying posts. Both options had "sort by date" as an option, although one had more sort options than the other.