If there are more than one NVMe disks connected, BIOS "Peripherals-> NVMe controller and Drive information" menu item shows wrong information.
In short, the first NVMe disk size is reported correctly, but the size for second NVMe disk is reported as ( size of disk 1 + size of disk 2 ). If there were three NVMe disks connected, most probably their sizes would be added on top each other. I did not try that, but you can / must try that case too.
In all cases I attached, MyDigitalSSD BPX 120 GB is attached on motherboard m.2 socket, the other NVMe disk is attached through Asus Hyper M.2 PCIe card installed in second PCIe x16 slot.
nvmeproblem01.jpg shows when only MyDigitalSSD BPX 120 GB is attached to m.2 socket. BPX size is reported as 120 GB.
nvmeproblem02.jpg shows when MyDigitalSSD BPX 120 GB is attached to m.2 socket and a second MyDigitalSSD BPX 120 GB is attached to PCIe slot. BPX size is reported as 240 GB.
nvmeproblem03.jpg shows when MyDigitalSSD BPX 120 GB is attached to m.2 socket and a second Lenovo 512 GB NVMe is attached to PCIe slot. BPX size is reported as 632 GB.
nvmeproblem04.jpg shows when MyDigitalSSD BPX 120 GB is attached to m.2 socket and a second Samsung 256 GB NVMe is attached to PCIe slot. BPX size is reported as 376 GB.
Windows reports size of each NVMe disk correctly and uses them correctly. What is displayed in BIOS NVMe menu is faulty.