I applied this 'fix' but it did nothing for me file explorer or start menu search problem.
I just figured out that there are still multiple issues, even with KB installed.
I.e.:
1) After a while, drop-down list of quick suggestions (if matches for a given directory do exist) stops to appear, you need to restart the OS to get this working again. Basically search only launches itself if you hit the "->" square at the right side.
2) If there's an external (additional) display connected to your system, once you move the Windows Explorer to that external display, open necessary parent folder and hit in the Search field, the overlay of white rectangles appears above the Search field,
and I even cannot see what I'm typing! (see attached image as an example of this).
3) Still not fixed the behavior of clear (x) icon. Expected behavior = clear the already entered search query, actual one = nothing happens at all (therefore I have to hit the "<-" icon at the navigation side of the window).
MS, please hire more decent qualified QA!
It's unbelievable to suffer from breaking such a basic feature for so long!