Windows 10 not showing in Grub

I'm brand new to Linux and I've set up a dual boot with my existing Windows 10 installation and a new Manjaro install but the option to use Windows doesn't exist in the Grub menu. I know it still exists and works fine as I can boot into it in the Bios but it doesn't show up in Grub. I have tried to update Grub and to use os-prober, both to no effect. I've even tried re-installing grub using this guide (https://wiki.manjaro.org/index.php?title=GRUB/Restore_the_GRUB_Bootloader). However this boot info script (http://bootinfoscript.sourceforge.net/) I found suggested in thread about someone with a similar issue detects it fine.
This is the output for fdisk -l

Disk /dev/nvme0n1: 465.78 GiB, 500107862016 bytes, 976773168 sectors
Disk model: Samsung SSD 970 EVO 500GB               
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xfdb43254

Device         Boot     Start       End   Sectors   Size Id Type
/dev/nvme0n1p1           2048 940677939 940675892 448.6G 83 Linux
/dev/nvme0n1p2      940677940 976772909  36094970  17.2G 82 Linux swap / Solaris




Disk /dev/sda: 931.53 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: Samsung SSD 860 
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 0680F5F4-E77F-44EC-97B9-B3863393368F

Device       Start        End    Sectors   Size Type
/dev/sda1     2048    1023999    1021952   499M Windows recovery environment
/dev/sda2  1024000    1226751     202752    99M EFI System
/dev/sda3  1226752    1259519      32768    16M Microsoft reserved
/dev/sda4  1259520 1953523711 1952264192 930.9G Microsoft basic data


Disk /dev/sdb: 931.53 GiB, 1000204886016 bytes, 1953525168 sectors
Disk model: Samsung SSD 860 
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 03C290E4-22BE-4D87-926D-A8E3A53D6987

Device     Start        End    Sectors   Size Type
/dev/sdb1     34      32767      32734    16M Microsoft reserved
/dev/sdb2  32768 1953521663 1953488896 931.5G Microsoft basic data

Manjaro is installed on the nvme drive, windows is on sda and sdb is just a drive I use to install games on.

Windows is in uefi
Manjaro is installed in bios-legacy.

You need to reinstall manjaro in uefi and make Samsung SSD gpt first.
Or you can continue as is.

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Thanks, but what exactly do I do differently (ie, how to I not do the exact same thing when re-installing?) I'm assuming there was an option somewhere I missed?

Read Manjaro User Manual.

When booting, use Quick Boot menu (UEFI) to select the UEFI USB option.

There is also another one without "UEFI" in option title, which boots in MSDOS/Legacy mode and that's how you ended up installing in MSDOS/Legacy mode.

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Generally...
if gpt, use uefi
if msdos, use bios-legacy
do not mix gpt and msdos disks
do not mix uefi and bios-legacy

bios-legacy grub (& other bootloaders) cannot boot uefi windows
uefi grub (& other bootloaders) cannot boot bios-legacy windows.
So linux and windows must be in same boot (uefi or bios-legacy) or end up like in your case

uefi grub can boot bios-legacy linux OS
bios-legacy grub can boot uefi linux OS's (with some tweaks and in some newer bios)
but can result in some issues in both cases if kernels are installed while in wrong boots
So generally, not advisable to mix uefi and bios-legacy linuxes.

bios-legacy can operate in gpt but with expert preparations (bios_grub, unallocated, first partition flagged) especially for bios-legacy only systems with > 2 TB disk.

So generally... for both novices and experts,
if gpt, use uefi
if msdos, use bios-legacy
do not mix gpt and msdos disks
do not mix uefi and bios-legacy

2 Likes

Here is the tutorial telling you almost all you need to know:

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