Comment # 1 on bug 1208584 from Lubos Kocman

Seems like the os-prober is present:

lkocman@localhost:~> sudo grep Windows /etc/grub.d/*
/etc/grub.d/30_os-prober:    Windows\ Vista*|Windows\ 7*|Windows\ Server\
2008*)

Just to specify my layout: (two nvme disks one Linux-only, the other one
Windows-only)

lkocman@localhost:~> sudo fdisk -l
Disk /dev/nvme1n1: 953,87 GiB, 1024209543168 bytes, 2000409264 sectors
Disk model: KINGSTON SKC3000S1024G                  
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: E0B91263-D7A9-4225-98A5-D03FFC8D538E

Device           Start        End    Sectors   Size Type
/dev/nvme1n1p1    2048    1050623    1048576   512M EFI System
/dev/nvme1n1p2 1050624 2000409230 1999358607 953,4G Linux filesystem


Disk /dev/nvme0n1: 1,82 TiB, 2000398934016 bytes, 3907029168 sectors
Disk model: KINGSTON SNV2S2000G                     
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: 01DE65FD-53B3-488F-8DE7-628D3F0230DC

Device          Start        End    Sectors  Size Type
/dev/nvme0n1p1   2048     206847     204800  100M EFI System
/dev/nvme0n1p2 206848     239615      32768   16M Microsoft reserved
/dev/nvme0n1p3 239616 3907025943 3906786328  1,8T Microsoft basic data
lkocman@localhost:~>