Ember 4.x (Octane) - replacement for Observers?

I am nearly done upgrading a very old Ember.js project from 2.13 all the way up to the latest LTS release, 4.12. Along the way I've been coming to grips with the changes that the Octane release brought about, and one area I'm struggling to adapt is our use of observers.

We use observers in two files to fire function calls when an observed value changes. I understand that Observers are discouraged in Octane, so if possible I'd like to migrate away from them.

My understanding is that tracked properties are the end-all be-all now; they're largely meant to replace computed properties, and I assume other state-based functions like observers, but I'm not really sure how to apply them in this use case, or if it's even possible.

My question is: Is there a preferred replacement for Observers in Ember Octane (4.x+)?