How do I show only the latest post from each user in a view?
The problem is that you are trying to filter based on two things:


Show the most recent content by an individual user.
Show each user.


In Views, you can generally only filter one kind of entity (content OR users) at a time.

However, there is a module that can help, Views Field View.  This module lets you embed one view inside another.

So, you can do something like this:


Create a view that shows the most recent content for a single user (takes a contextual filter of UID, returns one result, sorted by descending most recent).
Create another view that shows all users except the logged in user.  Use Views Field View module to embed the first view and show the most recent post by each user.


I haven't done this exact implementation before, but I've used Views Field View for similar things.  There is a tutorial here.

If you use this module, do note this warning from the documentation:


  Please note that using this module can impact the performance of your
  site, if the views being rendered are very resource-consuming. It's
  highly recommended to use this module in conjunction with other
  modules that provide views caching.
  
  Good candidates to cache your views are the modules Views content
  cache and Cache Actions.