What's up with Control Backspace, and Control Shift Z?

I cannot seem to remap them.

All the former does in Insert Mode is type Î, and then make the "z" letter show up in the statusbar.

And bafflingly, in Normal Mode, the latter opens a new instance of cmd within cmd.

In answers to other questions, I saw that VIM does not recognize Shift - or at least, that's the way I understood it.

Well, if it doesn't recognize Shift, then why is my remap of C-Z to Undo not triggered when I press Control Shift Z?

What's up with Control Backspace, and Control Shift Z for the Windows cmd terminal?

I cannot seem to remap them.

All the former does in Insert Mode is type Î, and then make the "z" letter show up in the statusbar.

And bafflingly, in Normal Mode, the latter opens a new instance of cmd within cmd.

In answers to other questions, I saw that VIM does not recognize Shift - or at least, that's the way I understood it.

Well, if it doesn't recognize Shift, then why is my remap of C-Z to Undo not triggered when I press Control Shift Z?