Thanks very much. This got things going. Interestingly, the 7Zip installer also requires Admin access, but using the tip from StefanHamminga, there is a portable version of 7Zip that I've added to the utilities on my USB drive.
I had a quick look at the KiCad path preferences and most point to C:\msys64 (which doesn't exist anyway). I presume that directory would have been created by the installer. I'll have a look into what I need to do to get that straightened out. It could be that I need to use the portable version that was linked above.
Need to use KiCadPortable to fix the paths.
Thanks again for the tips!