how to let `clear` command just clears the current screen

I use iTerm2 apps as my terminal option on my Mac computers. On my 1st Mac, when I type clear, it just clears out the current screen, and when I scroll up, it could still show the previous contents on this tab which I really like. On my 2nd Mac, however, when I type clear, it clears everything out of this tab. When I try to scroll up, there's nothing’s present. How can I make my 2nd Mac behave the same as my 1st one? I've checked every single configuration in between these two machines for iTerm and they look identical, both are using oh-my-zsh.