Powershell:
GWMI -namespace root\cimv2 -class win32_volume | FL -property DriveLetter, DeviceID, Label, FileSystem, SystemVolume, Capacity

mountvol /?

mountvol h: \\?\Volume{457ceece-2fce-11ed-a5a6-4889e78cc761}\

USB flash boot drive for HP Microserver Gen8:

Download the latest stable hybrid ISO from https://sourceforge.net/projects/supergrub2/
Use rufus to flash (as FAT). Don't use balenaEtcher to flash as that wil do some weird ISO partition format thingy which won't be mountable in Windows
Reboot with disk. Use sgd to auto-detect where Windows 10 is.
Copy commands and write to grub.cfg