Thanks for the motivation, it is more important than the solution after so many tries. I am surely backing your friend here in this weird challenge of my computer’s nerves :))).
That is understood, I also have MSVC2019 installed, and setting ninja off is using that MSVC successfully. The MSVC error appears as soon as I use ninja, which is made to improve installation speed (at the moment, with ninja set OFF, I guess it is about seven hours running time for a successful run and about three for an erroneous run). Up to now, I have installed from anaconda prompt, I will try your recommended Native tools command prompt for vs 2019 as soon as I find the time, probably in a few weeks only.