Taken right from your manual in the BIOS section for sata express, should have shown this in the sata tables or the PCIE combo port pages.
If its set to auto M2 is given priority when populated then SATA express and if neither is present then sata
Set to M2 Sata express is disabled and no SATA
Set to Sata express M2 is disabled and no SATA
Sorry but this looks like an either/or choice, cant have both.
“Two things are infinite: the universe and human stupidity, I'm not sure about the former” ~ Albert Einstein