If after you install an earlier version of Windows on a computer that already has a newer version of Windows, you may find that the name or entry for the newer version of Windows may be missing from the startup options or boot menu in the dual-boot computer.
Installed Windows entry missing from Boot Menu Options
Let us say as an example, if you install Windows 11 on a PC where Windows 10 is already installed, the Windows 11 boot menu incorporates the options from the older OS’s boot menu.
But, on the other hand, if you have installed Windows 10 on a Windows 11 machine, in the Boot Menu, you may no longer be able to see Windows 11 as an option. This occurs because when a different version of Windows is installed, it rewrites the MBR to call its own boot loader. It will overwrite the MBR with one that does not recognize the newer Windows Boot Loader.
You can resolve this issue, as follows. Boot into the older Windows version, whose name or entry appears and open an elevated command prompt window. Type the following and hit Enter:
Run <D>:\Boot\ Bootsect.exe –NT60 All
Where <D> is the Drive letter. Reboot.
You will now be able to see the menu option/s for the newer version of Windows.
Now To restore the entry for the older version, open an elevated command prompt, type the following and hit Enter:
Bcdedit –create {ntldr} –d “Put Description of Menu here”
Restart Computer.
This works for Windows 11/10/8/7.
Related: Choose an operating system screen or Dual boot menu missing.