mintty focus problem after Windows 11 Insider Preview update

[Bruce Jerrick]

I am not able to reproduce the mintty window focus problem.
(Also I failed to mention that I was originally using the latest
  test version of the cygwin package, but that now appears not
  to matter (see below).)

Test history is as follows.  Versions not mentioned are the same
  as the previous stage.  The Windoze updates/reversions involved
  the usual (for Microsoft) reboot.

1. Originally; problem was not present:
    Windows 11 Home Version 23H2 build 22635.4000 (KB5040546)
    cygwin 3.6.0-0.153.g1fb17a4b2d54  (test version)
    mintty 3.7.4-1

2. Problem occurred after update to:
    Windows 11 Home Version 23H2 build 22635.4005 (KB5040555)

3. Problem disappeared after reverting that update back to:
    Windows 11 Home Version 23H2 build 22635.4000 (KB5040546)

Two days later:

4. Problem did not re-appear after reverting to:
    cygwin 3.5.3-1  (release version)
   and re-updating to:
    Windows 11 Home Version 23H2 build 22635.4005 (KB5040555)
Which made me think that (maybe) the test version of cygwin was
  the problem.
But then:

5. Problem did not re-appear after re-updating to:
    cygwin 3.6.0-0.153.g1fb17a4b2d54  (test version)
Which brings it all back to the same state as stage 2 above.