If manually add a variable to define the issue number in your pipeline is workable. You can try below to add a bash task at the end of your release pipeline and call Jira api to transition the issue status.
First define a variable for issue number, and one for transitionid if neccessary.
Second add a bash task at the end of your release pipeline.
Assume you know your transition ids. You can use below script.
click here to get your api token for your Jira.
curl -D- -u "username:APIToken" -X POST --data '{"transition":{"id":"transitionid"}}' -H "Content-Type: application/json" https://[accouint].atlassian.net/rest/api/2/issue/[issue-no]/transitions?transitionId?expand=transitions.fields
(To get transitionids use below api):
curl -D- -u "username:APIToken" -X GET https://[accouint].atlassian.net/rest/api/2/issue/[issue-no]/transitions?transitionId?expand=transitions.fields
Update:
Pull request title can be retrieved via below rest api.
GET https://dev.azure.com/{organization}/{project}/_apis/git/repositories/{repositoryId}/pullrequests/{pullRequestId}?api-version=5.1
Hope above is helpful to you.