iTerm2 - How to show alternate screen in iTerm2?
By searching the one page documentation of iTerm2 for each occurrence of the expression alternate screen, we can deduce that this feature is not yet implemented in iTerm2 3.2.0.

== EDIT ==

Here is a feature request on the Gitlab repository of iterm2.

== EDIT (2) ==

The feature has been implemented with commit 7b8d6a4b4. You can already test it in the nightly build in the Session > Terminal State menu.

According to George Nachman (the maintainer):


  There is no shortcut (I'm basically out of shortcuts) but you can always assign one in Prefs > Keys.


Thanks to him for this new feature!