New here and been fighting this all day.
Turns out my 1TB Crucial P310 PCIe Gen4 M.2 does not work inside the PiMon5 Max case but will via USB / NVMe Enclosure. Which beats the objective really.
Had an old Sandisk 256GB NVMe laying around to test and this works inside the case.
Reluctant to spend anymore money to get this working, but I need at least 1TB.