Windows Boot Manager is a tool that enables you to load multiple operating systems on your computer. This can include multiple versions of Windows or different operating systems entirely. If you're ...

if you want to "get rid" of Grub, you can use dd to copy a bunch of 0's to the MBR, but I bet you don't want to do that ;p Anyway, my best recommendation would be to boot to linux and type "info grub" ...

It sounds to me like claiming that all old Windows versions will be unbootable is an overstatement. Rather, it's most likely the case that you won't be able to boot old media when Secure Boot is ...