Many times just doing an update-grub may find Windows and add it to grub, but a lot of times it won't.
Create Windows in a custom grub entry like below:
sudo vi /etc/grub.d/40_custom
menuentry "Windows 10" {
set root='(hd0,0)'
chainloader + 1
}
Change Windows 10 to whatever you want to call it. For example if it was for Windows 11 you'd probably want to ca........