Copying a sheet from a different diagram

Please open the diagram you want to copy elements from and a blank diagram.

Select everything on the sheet you want to copy by using the keyboard shortcut Ctrl + A (Command⌘+A for Mac), then copy all objects by Ctrl + C (Command⌘+C).

Go to the target sheet of the new diagram and paste the copied contents using Ctrl +V (Command⌘+V).