Update GRUB Not See Windows
First, you need to check BIOS/UEFI settings
In general, GRUB settings are made in the BIOS. And then they can be fixated by the command:
sudo update-grub
to linux.
When the Windows bootloader is failed
The Windows bootloader may also break. I can test if it works by inserting my 8Gb Live CD/Flash with Windows.iso, and then using the command in cmd:
bcdboot c:\windows /s c: /l en-us
and we fix it right here with 4 short commands:
bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd
and then restart bootloader again:
bcdboot c: \windows /s c: l en-us
If after bootrec /fixboot you get the message:
... access denied
you need to change BIOS/UEFI settings
If after sudo update-grub you get ouptut with this line at the end:
...
Windows Recovery Environment (on /dev/nvme0n1p1)
It's ok. Your GRUB menu is setup correctly. Reboot and try starting Windows via GRUB.
When Windows bootloader is fine
When windows bootloader is working and the correct order of disks is set in the BIOS, then sudo update-grub should see windows. If not, you can try to go intoKDE Partition Manager and mount the disk partition by adding a mount point (more about this in my docusaurus post: https://papa31.github.io/hm/docs/new-disk/partitioning-new-disk/#kde-partition-manager)
Learn more about setting up GRUB here (my OneNote post): https://1drv.ms/u/s!ArW_zB-uhr61g-5wDrlhlrNRyKLeVQ?e=799eVC