This message appears to be during install of a board manager package. Either the package does not have a windows toolchain or there was an unpack (unzip) problem during install.

What is the url of the package index json that you have installed? This can be seen at the bottom of "Micro platform > IDE Locations"

I removed the following from Arduino IDE 2 additional boards manager because VM threw up a different message referencing the URL: https://github.com/digistump/arduino-boards-index/blob/master/package_digistump_...

I have now replaced the URL, let AIDE2 do it's update thing and the error seems to have gone away.  I've attached a couple of screen shots of what I think you were asking for? I have not added any URLs to VM Optional Boards Manager as I assumed VM would pick them up from AIDE2?

Thanks for the update re the correct URL for digistump and now I can see the difference viewing the incorrect and correct versions online.  I updated the additional URLs in AIDE2 to reflect the correct URL.  However I was still getting error messages about missing UF2 files  et cetera, so I tried adding the list of additional URLs to the VM IDE locations page (correctly formatted with ,) but this caused VS to crash if I clicked rescan or check for updates (post crash error message attached).  For no particular reason I decided to add a new board, the two UNO R4 boards and then restarted VS and all the problems disappeared i.e. the very slow response clicking anything in Micro Explorer, the error messages and the VS crashes - no idea why but a big relief.  I have attached the build properties output as per your request, in case you need it, and will do so in future.