The usb install was created using microsofts tool for that. As for the disk, I nuked it, change to GPT and reinstalled,after which I looked at the partition scheme and found that although it’s clearly UEFI, it’s not GPT.
I suppose you’re right that the USB was booted in old school mode, but why on earth was an EFI partition created then?
At any rate, I didn’t have other boot option in “BIOS”, though it is possible that legacy is enabled.
Your idea of adding the USB to Grub to force UEFI boot is not a bad idea, but I’ll investigate other options first.
I’ll see what I can do when I get home from work tomorrow and return with the result.
Update:
So as it happens, I’ve come somewhat closer to an answer
I was massing about in BIOS, or whatever you call it these days, and when I chose to boot only EFI, only the Windows install was available, and when I chose to boot only legacy, only that Linux install was available.
The answer is obvious of course. For some reason I cannot begin to comprehend,Linux wasn’t installed as EFI, and Windows was, although it insist on not being GPT, while the Linux install works perfectly from GPT.
I can’t say I quite understand, but at any rate the solution is simple. I’m gonna nuke both disks and ensure they’re GTP, then I’m going to reinstall Windows, ensuring to boot in UEFI mode, and them I’m gonna reinstall Linux, again ensuring to boot in UEFI mode.
Assuming that everything works as intended, The problem should be solved. It’s a bit more work than I’d hoped for, but at least there’s nothing much to backup, and the installs are uncomplicated and relatively quick.
Just think MBR is Master Boot Record and to be a master you´re required to be old (obviously), because otherwise you ain´t got experience. BIOS is the old thing.
The partition scheme is MBR, if that’s what it’s called, but it boot like EUFI, that’s what so weird. I think MBR can be included in GPT, so the other way around it’s not that weird, it’s just stupid.
So I’ve done what I’ve set out to do, and os-proper now finds Windows and update-grub adds it to the Grub menu.
However, it doesn’t actually boot Windows. some missing file or rather.
It does refer to the correct partition, the EFI partition I should think is the right one.
So, as it is now, a lot of work with no real result, but I’m sure I’ll figure out what’s wrong.
edit:
more specifically the error message reads:
error: no such device: 864D4239
error: file ‘/efi/Microsoft/Boot/bootmgfw.efi’ not found
It seems to me that the uuid is fishy, but it is correct according to lsblk.
Yeah, fast boot screwed my last dual boot. As of now, I only dual boot to use windows since I’m homeless and don’t have another pc to use at the moment.