HPC sales here. Realistically, I don't think we've designed or sold a Microsoft HPC cluster in... Maybe 5+ years now?

We've done plenty of HyperV clusters and the like, and those are typical and great for Windows environments, but when it comes to compute, it turns into a sanity question - why would you pay far more (licensing) for lower performance and less control?

Unless you're running commercial closed source code that's Windows only (which to be fair may exist, but I have never personally seen for HPC clusters)... I would recommend sticking with Linux.

If you're running your own custom/modified code as most HPC teams do, then it's a pretty quick recompile and then you're off to the races on Linux. Yes, things will look different, but if users are used to working in a custom application, it's going to be the same application on linux.