I followed this
to remove Ubuntu 20.4.1 LTS and grub2 - the answer with the most upvotes.
After that grub2 black screen is gone but Windows 10 is not booting.
Update1
I logged in using live USB and then tried boot-repair. Followed all the recommendations by it. It tried to reinstall grub2 so there seems to be another Ubuntu Linux 20.4 some where being installed on my computer(I have 1 NVME PCIe drive where Ubuntu Linux was installed - which i deleted, then 1 SSD where Windows is installed i.e. Windows C drive and then two hard drives for Windows D and E). It seems somewhere on C, D or E - ubuntu linux is installed and i want to get rid of it OR move to PCIe NVME drive Here is the boot-repair output link and contents from boot-repair activity:
You can now reboot your computer.
Please do not forget to make your UEFI firmware boot on the Ubuntu 20.04.1 LTS entry (sdb2/EFI/ubuntu/shimx64.efi file) !
If your computer reboots directly into Windows, try to change the boot order in your UEFI firmware.
If your UEFI firmware does not allow to change the boot order, change the default boot entry of the Windows bootloader.
For example you can boot into Windows, then type the following command in an admin command prompt:
bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi
Here is the gparted view from my Ubuntu Linux 20.4 LTS
There is somehow hidden Ubuntu 20.4 LTS being installed some where else also which is making my grub to boot into Ubuntu 20.4 LTS Linux.
Update 2
After some more searching and digging, found that another copy of Ubuntu Linxu 20.4.1 LTS is installed on /dev/sda7
and also confirmed by df command
root@ashu-XPS-8930:/home/ashu# df
Filesystem 1K-blocks Used Available Use% Mounted on
udev 32757028 0 32757028 0% /dev
tmpfs 6557040 2188 6554852 1% /run
/dev/sda7 95099332 8980340 81245112 10% /
tmpfs 32785188 126668 32658520 1% /dev/shm
tmpfs 5120 4 5116 1% /run/lock
tmpfs 32785188 0 32785188 0% /sys/fs/cgroup
/dev/loop0 98944 98944 0 100% /snap/core/9804
/dev/loop1 9344 9344 0 100% /snap/canonical-livepatch/95
/dev/loop2 56320 56320 0 100% /snap/core18/1880
/dev/loop5 30720 30720 0 100% /snap/snapd/8542
/dev/loop4 261760 261760 0 100% /snap/gnome-3-34-1804/36
/dev/loop3 63616 63616 0 100% /snap/gtk-common-themes/1506
/dev/loop6 51072 51072 0 100% /snap/snap-store/467
/dev/sda2 98304 61255 37049 63% /boot/efi
tmpfs 6557036 20 6557016 1% /run/user/125
tmpfs 6557036 32 6557004 1% /run/user/1000
Update 3 Even after deleting /dev/sda7 partition from Windows and then deleting /EFI/ubuntu - i was not able to make Windows 10 boot. Thus used the live USB drive to copy the important data from Windows C: into Windows D: Later used the Windows recovery drive to reinstall the Windows on C: drive. I could have installed it on other drive but my C: is SSD and i prefer installing OS and apps on faster media.
Well in the end this was not successful:
only thing which worked was: to install Windows 10(after trying 1 and 2) using the recovery media. Prior to that - I connected the data cable/Ubuntu live USB to take some back as Windows installation will wipe clean the C: Drive. Other drives - D and E were intact and require nothing from my side.
After that installed Ubuntu 20.4.1 LTS alongside Windows 10 on my PCI NVME hard drive. Live USB was created to boot into UEFI mode and BIOS was with UEFI(disabled Legacy mode and secure boot also disabled). Ubuntu Installation was totally smooth - everything running fine now.
Somehow for me dual boot Windows/Ubuntu - Ubuntu upgrade from previous LTS to new LTS release never happened successfully. Same happened when i tried to upgrade dual boot Windows 7 or 10/Ubutnu 16.04 LTS to Ubuntu 18.04 LTS. While inplace Windows upgrade worked fine.