Should pull_request_target event fire with owner PR?

I am trying to figure out how to change an action from using pull_request event to pull_request_target, though it seems the action never triggers when pull_request_target is used.

I am starting with a very basic trigger:

name: PullReq CI

on:
  pull_request_target

When I update my PR the action doesn’t run. If I change pull_request_target back to pull_request the action fires okay.

I have read that pull_request_target works from the base, no merge, but honestly I don’t understand what that means and how it affects the event.

All I want to achieve is the ability to vet a new incoming PR and have an action run on it, like pull_request did back in the day. We have always validated incoming code before allowing external contributor code to run an action