How to use shift+alt+arrow-down for copy the selected lines just under the selected lines in Visual Studio Code

Previously I used Windows 10 operating system. I am a beginner and I am learning HTML, CSS. I used Visual Studio Code on Windows 10. There I used the shift + alt + arrow-down key to duplicate some selected lines just under the selected lines. I recently shifted to Ubuntu and the shift + alt + arrow-down key is not working like windows. It is not duplicating the selected lines.

How can I make these keys working like windows or is there any other key to do the same work?

Help me, please.

On Linux you have to hold Ctrl as well. Ctrl + Shift + Alt + Down

Linux software often avoids key combinations that use Alt on its own because Linux desktops often capture the Alt key for other uses.