Which CPU are you using?
Which PCIe slots are populated?
OS?
manual page 23, seems to indicate it should supports a SSD
M.2 / U.2 Slot BreakdownM.2 Lane Distribution*
M.2 Key-M (110mm, Top, M.2_1) – Gen4 x4 from CPU
o This slot supports PCIe M.2 SSDs / Intel® Optane.
M.2 Key-M (110mm, Middle, M.2_2) – Gen4 x4 from Z690 PCH
o This slot supports PCIe M.2 SSDs / Intel® Optane
M.2 Key-M (110mm, Bottom, M.2_3) – Gen4 x4 from Z690 PCH
o This slot supports PCIe M.2 SSDs / Intel® Optane
M.2 Key-E (32mm) – Gen1 x1 from Z690 PCH
o This slot is pre-installed with the EVGA Wi-Fi/BT Module
*M.2 Enable/Disable can be configured within the BIOS