I have tried 2 different ways to install dual boot operating system, and both worked.
Although, I don't know which one should I install first, windows or Ubuntu. what is the consideration?
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Install Windows first. Windows will overwrite the whole disk. Also, Windows will want to install its own bootloader, overwriting GRUB.
Then use Windows Disk Management to shrink the Windows NTFS partition.
Now you can install Ubuntu. Select the option to "Install alongside Windows" at the beginning of the installation process.