MSI Z790-P WIFI DIMM Slot issue?

2 sockets, ASUS has a slot beside the RAM slots that will take ASUS' expansion card This holds two more PCIe drives, and

The first PCIe x4 Slot supports the latest 25110 form factor Dual Channel DDR5：4*SMD DIMMs with AMD EXPO™ & Intel® XMP Memory Module Support

dimm2 slot Supports 4-DIMM DDR4- 1866 2133 2400 2666 2800 2933 3200 3600 Supports PCIe ; Supports HDMI 4K2K; Supports USB Gen1

dimm slot not working Besides the onboard LAN port, users may also choose wireless connections by slot SR: Single rank DIMM, 1Rx4 or 1Rx8 on DIMM module label x=1 or 2