Windows not discoverable by GRUB

Hello everyone. As per my post in Thoughts section, I followed in love with Ubuntu MATE, but the software that I'm using for my job, forces me to dual boot it with Windows 10. I used to have Ubuntu 18.04 LTS and after few replies on my topic, I decided to upgrade to 20.04 LTS. When I installed Ubuntu 20.04 LTS 64-Bit on my laptop, when it was about to finish the installation, I received an error when it was installing the GRUB Bootloader.
Powering on my laptop now, boots straight to Ubuntu MATE, without giving me the option to choose if I want to boot to Windows. I think somehow the Windows Boot Manager is messed up and that's why GRUB cannot find it.

I have tried using "sudo os-prober" / "sudo update-grub" / "boot-repair" / "grub-customizer" . None of this allows me to boot back into Windows.

Does anyone know how can I fix the Windows EFI from Ubuntu MATE and how to get it back in GRUB so I can boot into it?

Thank you and Happy Holidays everyone! Wish you all the best.

can you post output of lsblk -fs

iAME FSTYPE LABEL UUID                                 FSAVAIL FSUSE% MOUNTPOINT

squash 0 100% /snap/core
squash 0 100% /snap/snap
squash 0 100% /snap/core
squash 0 100% /snap/soft
squash 0 100% /snap/ubun
squash 0 100% /snap/ubun
squash 0 100% /snap/snap
sda1 ext4 e9ce14c3-43f3-4cf9-bdc9-5451ab893d97 74,9G 13% /

sda2 vfat 5A6F-347F 134,1M 29% /boot/efi

sda3 ntfs F4664D38664CFCBC

sda4 ntfs WinKit
│ 1E08ADB508AD8BF9

sd4 NTFS WinKit it's my D: drive in Windows containing all the software kits for my job.
sda3 NTFS It's my Windows drive ( C: )
sda2 vfat Not exactly sure what that is. Looks more like where the GRUB files or Windows Boot manager files are stored. Not sure about that.
sda1 ext4 It's my Ubuntu MATE drive.

sudo fsck -y /dev/sda3
sudo fsck -y /dev/sda4
(to clean up the win partitions)

sudo apt install os-prober
(in case you don't have it)

sudo update-grub
(should find win OS and upon reboot, the grub menu should let you select which OS to boot).


Good evening and thank you for all your help. After following what you said, now it works great and I hope it stays this way.

:beers: :beers: :beer: