Both M.2s appeared as options to install Windows to, but now that Win10 is installed, the second M.2 doesn't appear. The M.2s are 250+500GB Samsung 970 EVO Plus.
Hope this helps
Thank you, but the problem solved itself (see below). The drive was not showing up in BIOS even though it showed up when I initially installed Windows. I tried reseating it. I've owned my own tech company for over 10 years, so I had already covered the basics. I conveniently had 2 of each piece of hardware to troubleshoot.