Z390- new SSD not detected...

I'm not sure what I'm doing wrong. I have the z390 pro wifi. I have one NVME installed and 3 SSDs connected. I tried adding a 4th SSD, however i can't seem to find it.

I read that I should be able to have 6 total drives, so not sure what the problem is. Could the problem with my new SSD be on a port that is deactivated because of the NVME drive?

I used the only drive I could see with my graphics card hiding the other slots