Change the ticket status after pull request is completed

So this is actually in Azure Devops now - Set Work Item State in Pull Request

Don't use Complete linked work items after merging if you don't want the Work Item to be closed. ;)

To set the status of Work Item 123 to resolved instead of closed, in your PR description write:

Resolved: #123

This feature is useful if you want change multiple tickets and uses the syntax {state value}: #ID. For example, to close a Task and resolve a User Story at the same time.

Resolved: #123
Closed: #456

However it does rely on developers knowing and using the convention instead of it being a managed policy across the organisation.

Yes, agree with Shayki's answer. There does not such feature support by Azure Devops. Until now, this is a fixed option that you just can change it as completed while you complete the PR.

But, as work around, you can install an extension WorkItem Updater which can change work item while build executed. And then, add the task WorkItem Updater into your build. In that task, you can change it as any state you want.

I know, this is not convenience for you to achieve what you want.

But also, here has an UserVoice raised on Microsoft Developer Community which is our main forum for product feature suggestions : Customize Work Item State after PR is closed.

Note: You can vote and add your comment there. This UserVoice is already Under Review, I believe it will be meet soon.