Problem with Grub not showing all disks or partitions. This was after trying to install Garuda OS. As I seemed to have had to change the BIOS setting from Legacy-UEFI mode to just UEFI. I did this and installed Garuda but had various issues with it and uninstalled. I replaced it with trusty Mint 20.1. So on starting the computer the Grub shows Mint and Ubuntu in the list but does not show Windows 10.
I returned the Bios to Legacy-UEFI prior to installing Mint, as the Bios was not showing all the Disks, now it does but not on Grub. I tried a Boot Disk repair but this made no difference.
Here is the setup
sda1 Ubuntu
sdb1 Linux Mint
sdac1 Backup Disk
sdd1 EFI fat32
sdd2 Microsoft Reserved
sdd3 Basic data
sdd4 NTFS (No other label)

I am running a AMD Ryzen 5 2400 G
Bios MSi Click Bios 5

I need advice on how to reset the system so it shows all disks on Grub.

Any advice most gratefully received
Stephen

The grub menu does not show disks or partitions, it shows a list of operating systems to boot when the system starts.

Usually one operating system has "control" over the boot loader with a dual+ boot system and you can update its menu configuration via the update-grub command.

https://itsfoss.com/update-grub/

Postscript: Technically grub can show disks and partitions but that is from its command line interface but I am assuming it not the question.

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What partition and type grub is installed on will affect what it can see. I suspect that when you installed Mint it installed as UEFI, so you cannot see Windows on the old bios partition. Or vise-versa, Mint is old bios partition and Windows is UEFI.
I had an issue like this setting up dual boot when the bios was set to legacy-uefi. Windows would install in one format, and Linux in the other and grub would only see OS.
Set the bios to one mode or the other for dual booting, not both.

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+1 utek.
Bit interesting that Win10 was in legacy-UEFI - might imply it was an upgrade from Win7 at some time past.

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open a terminal and post the output of the following:

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You might find simply running update-grub or grub-mkconfig from Mint or Ubuntu will regenerate the boot menu and include Windows. First ensure os-prober is not disabled in each's /etc/default/grub.

Having both Mint and Ubuntu on the same UEFI PC can be troublesome. Both by default use the same filenames on the ESP partition, in a directory named ubuntu. This facilitates each usurping boot control from the other every time a new kernel is installed, or otherwise os-prober is run. Each can be made unique via GRUB_DISTRIBUTOR= in /etc/default/grub. Simply replace the content between the quote marks with any unique string you choose, such as ubuntu2004 or mint21, then perform a Grub update. The consequence will be each using a unique directory on the ESP. It won't stop outright usurpation, but other perplexing boot anomalies may be avoided.

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Thank you to all those that have written a reply. I did try some of the suggestions and I think UTECK is probably correct. My only problem now is which OS to delete and reinstall, with the correct settings.

Best wishes to you all.
Stephen