I just tried this is in a Virtual machine (I've not really bitten the bullet with Windows 11 yet...)
The older version of .NET doesn't seem to be installed by default (and previously we ascertained that .NET programs use the version they were built to run against, rather than the latest).
(followed by the Picaxe Editor installer aborting).
Rather than searching for said 'free download', I enabled "
.NET Framework 3.5 (includes .NET 2.0 and 3.0)" in Control Panel:-
and that did the trick