Good information that other users can benefit from!
I added a Crucial P5 Plus 1TB PCIe 4.0 3D NAND NVME M.2 SSD using a RIITOP NVME Adapter to the PCIe X16 mechanical X8 electrical slot PCIe Gen4 (SLOT 4).  The following are the Crystal Disk speed test:  [IMAGE] I experienced no error messages.  Seems to be completely compatible with the R12. The Crucial P5 is not the fastest Gen 4 NVME m.2 SSD, but it's a good value and it's faster than anything I've ever owned! It also shows SLOT 4 is truly Gen 4 capable.
Aurora R12, Crucial P5 NVME M.2 SSD testing result