I tried to check for a cmake update, but "choco install git cmake.portable strawberryperl -y", which is also claimed to be useful for updating them, does not think there is anything to update.
I then went one step back to try to see going to the chocolatey web page and install it again would work. Firstly, that web page has changed, so the command you're instructed to locate isn't present (i.e. the Compile.html document needs to be update). Secondly, using the "choco upgrade chocolatey" command buried in the script for when it's already installed does not upgrade the cmake.portable version past v3.16.2 (I didn't note what version it used before running that command, so it may or may not have been the same), which is lower than the one required.
Trying to run the installation script resulted in the expected result, i.e. refusal to proceed due to the presence of an earlier installation and the recommendation to run the upgrade command.
Ah, bugger. "choco upgrade chocolatey" apparently only upgrades itself, not any of its sub packages. "choco find cmake" shows that it actually "knows" about newer versions that the higher level installation decided not to mention were available, in favor for what was installed. Thus "choco upgrade cmake.portable" actually installs a current version. Presumably the same manual upgrade process has to be applied to git and strawberryperl as well. It's possible "choco upgrade all --noop" might do this in one go, but I haven't tried it (I'm just finding choco commands in choco.summary.log, trying to find what needs/can be done).
Well, strawberryperl doesn't want to be updated on my system, so I'll just leave it be.
I'm currently at the stage where I'm actually able to generate DFHack. Hopefully this rambling might be helpful to someone else trying to upgrade to the current standard.
Thanks to @ab9rf for identifying the root of the issue.
Edit:
OK, it looks like I'm stuck for the time being. DFHack doesn't seem to recognize the Classic version, which is what I'd intended to use until keyboard support has been restored (at which time I intend to buy it via Itch.io, not Steam, which may have a different layout from the 4 steam versions it seems to recognize, based on the stderr.log contents).