Closure is a healing process.
It usually takes some time and the right conditions.
It doesn’t make memories go away but you can feel good again, you can feel relief from the pain of loss.
I think closure is a shift in peace of mind, as returning comfort is to an injury as it heals.
You could end up good as new, but it will be hard to pin a moment on the finished healing.
Instead you’ll feel closure events when you can do something you couldn’t while the injury and pain were still there.
The one who initiates the break-up is likely to feel closures earlier there can be tipping points in a relationship from which there is no return. When decisions are made to end the relationship, it’s part of the path to closure for that person.
The initiator could feel a closure kind of experience when someone moves and the spouses are in separate residences, someone’s stuff is moved to another address.
Another might be a legal separation judgement prior to a divorce that help free a spouse from financial abuse along with separation from physical abuse.
If you have kids it must be a milestone when they are old enough to not need either of your supervision, reducing the requirement of regular communication.
When the other one starts dating someone else, or marries someone else, or moves to another city.
When you start dating someone else, or marry someone else, or move to another city.
If support payments stop that’s a real milestone and would be some real closure for the payer.
If you’re good friends after the divorce then a lot of these things will be shared milestones not closure events.