Is it possible to detect if an action was taken in an output apply? i.e. create, update

you mean like

// pseudo code
const resource1 = new pulumi.resource()
resource.apply(val => {
   const resource2 = new pulumi.resource()
})

and see if resource 2 gets updated?

No. I know you can’t create resources inside an apply. What I am looking to do is perform a validation inside of an apply something like this:

resource.apply(val => {
  if (val.wasCreate() || val.wasUpdate()) {
     validate(val)
  }
})

oh that's interesting. I see what you're getting at. I have never tried something like that. what is the downside of validating even if the resource wasn't updated?