OK, I (finally!) got Audacity 2.4.2 with ASIO to compile on Windows 10.
I would like to share with you my steps, so that you may/might be able to duplicate them. My thanks to steve, Apesbrain and micsthepick whose posts gave me the solution I only had to duplicate and document; and to Steve A Lee for the 2.4.1 version of this cmd file.
1) I have previously download Visual Studio Community Edition 2017. See https://visualstudio.microsoft.com/vs/older-downloads/
2) I have previously downloaded and intstalled git; if you haven't done this do this now. See https://git-scm.com/download/win
3) Download and install win32 installer for cmake-3.19.1 from https://cmake.org/download/
4) Download current python 3.9 from https://www.python.org/downloads/windows/
5) Create c:\proj242 directory
6) Download latest ASIO SDK from https://www.steinberg.net/en/company/developers.html
then unzip the ASIO SDK folder and move the folder to c:\proj242.
7) Rename this folder to "ASIOSDK"
8) copy the following code build-audacity.txt to c:\proj242\build-audacity.cmd
[Note .cmd extension!]
This will download the source code for audacity widgets, audacity 2.4.2, then compile, cmake, and build everything.
9) copy the next segment of code and save it to c:\proj242\asio2.patch
10) There should be two files and one folder in c:\proj242:
11) Press Windows-R and type "cmd"
12) type "cd c:\proj242", then type "build-audacity"
13) The compiled progam will be built to C:\proj242\audacity\win\bin\Release\Audacity.exe