Not sure if this what you mean: If you're using the command Palette, Copy Lines Down (Ctrl +Shift + D) requires that you select the entire line, but if you use the keyboard shortcut Alt + Cmd + Up/Down, it does not; your cursor can be anywhere on the line.
Thanks for the reply. I just want to copy the entire line in the copy buffer because I want to paste it somewhere else. What you described is a very specific use of the copy line shortcut. Most editors let you copy the entire line without selecting it.