Per the service manual, it's B550A.  CPUz is a third party software, it is just picking it up incorrectly. The M2 drive runs at pcie 3.0 x4 speed.  That is also in the Dell specs and confirmed by a number of users.  
Hello, I recently bought a Aurora R10 with a 5600x, to my surprise under CPU-Z the motherboard that ships with this configuration is an X570. Under GPU It does state that its running at PCIE 4.0 compatibility. I didn't buy a SSD from dell with my PC so I was wondering if I bought a PCIE 4.0 NVME SSD, would it sustain PCIE 4.0 speeds?
Alienware R10 5600x PCIE 4 Compatability?