@hikari You'll have to recreate the Windows bootloader if you used gdisk (Windows has a tool that can convert MBR to GPT which also automatically writes the new bootloader – it's called mbr2gpt, and you can run it from install media).

What you need to do:

• first make an EFI system partition (ESP) and format it to FAT32, it should be 100-300 MB in size; then boot any recent Windows install medium, and once it's booted press Shift+F10 – this will give you a command prompt.
• run diskpart, type lis dis (which will list all disks in your machine), then sel dis X (replace X with your NVMe drive number); lis par (shows partitions), sel par X (replace X with ESP number), assign (assigns a drive letter to ESP, since it doesn't have it by default); lis vol (lists drive letters, you should now see which drive letter is your Windows partition, and which drive letter is ESP); exit (return to cmd.exe)
• verify Windows partition drive letter with dir Y:
• finally write the Windows bootloader with bcdboot Y:\windows /s Z: /f UEFI (Y: is your Windows partition, Z: is your ESP)
• reboot with wpeutil reboot, and Windows should now boot

@jernej__s that probably would've worked! but i'm doing my own weird thing now instead