Hi Rahul,

approver_user has pretty much been transitioned in to business_stakeholder on most new contracts/renewals you'll start to see the business stakeholder roles coming in.

Hence business_stakeholder role is the key role that needs to be given to user's who wants to approve a request.

Kindly refer below articles for reference.

https://community.servicenow.com/community?id=community_question&sys_id=577eb50ddbe66050d5c4d9d9689619eb

https://docs.servicenow.com/bundle/sandiego-it-service-management/page/reuse/itsm/reference/installed-with-business-stakeholder.html

Regards,

Deepankar Mathur