Identified cause of potential pg_upgrade failure on Windows due to OS update adding partial block list of ports 50xxxx (could not connect to server)

I'm a PostgreSQL user on Windows and encountered trouble running pg_upgrade with the following error [1], ultimately due to blocked ports in Windows added via OS updates.

A workaround is to run pg_upgrade with lower range ports for the old/new servers via the -p/-P parameters.

##################################

> pg_upgrade

Performing Consistency Checks
-----------------------------
Checking cluster versions                                   ok

*failure*
Consult the last few lines of "pg_upgrade_server_start.log" or "pg_upgrade_server.log" for
the probable cause of the failure.

connection to database failed: could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 50432?
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 50432?
could not connect to source postmaster started with the command:
"C:/program files/postgresql/12/bin/pg_ctl" -w -l "pg_upgrade_server.log" -D "C:/program files/postgresql/12/data" -o "-p 50432 -b " start

The root cause is that pg_upgrade wants to start a pg server instance on port 50432, which is in the Windows port block list as of (I believe) KB4074588 (see https://support.microsoft.com/en-us/topic/february-13-2018-kb4074588-os-build-16299-248-b4e2ca66-dd7a-6fd5-a8f3-dc6683d4922b and https://superuser.com/a/1504618/74693)

The block list as of writing for me is:

Protocol tcp Port Exclusion Ranges

Start Port    End Port
----------    --------
      5357        5357
     44376       44376
     49683       49782
     49783       49882
     49883       49982
     50000       50059     *
     50265       50364
     50370       50469
     50849       50948
     51049       51148
     51149       51248
     51349       51448
     51449       51548
     51549       51648
     51649       51748
     56959       57058
     57059       57158
     62662       62662

* - Administered port exclusions.

I've seen previous people report trouble with this problem without an obvious resolution (see https://www.postgresql-archive.org/Upgrade-9-4-to-12-on-windows-system-td6163643.html and https://community.microfocus.com/cyberres/idm/f/idm_discussion/301027/pg_upgrade-fails-on-windows-2012r2-when-updating-to-idm-4-6).

A silly problem, but perhaps pg_upgrade could look to use different ports not in the Windows block list to prevent this issue.

Kind regards,

Andrew