The ability to track stakeholders and team members working on an opportunity is a feature available within D365 sales. The Stakeholders and Sales Team subgrid on the out-of-the-box Opportunity form lets you do that.
In D365 Sales
The Stakeholders subgrid uses connections to associate contact records as stakeholders with the opportunity.
This creates a connection record between the opportunity and the contact by using the Stakeholder connection role. You can change the connection role to any other applicable stakeholder connection role by opening the record and changing the As this role field on the connection record. Other out-of-the-box connection roles configured under the Stakeholder connection role category are Champion, Decision Maker, End User, Economic Buyer, Influencer, and Technical Buyer. However, The Stakeholders subgrid on the Opportunity form only shows connections that have a connection role category of Stakeholder.
Sales Team Subgrid:
You can add existing users as sales team members by using the Sales team subgrid. The Sales team subgrid also uses connections to associate users with the opportunity in different sales member roles. Similar to adding a stakeholder, you can add an existing user as a sales team member by using a connection. Other out-of-the-box connection roles configured under the Sales team connection role category are Delivery Professional, Account Manager, Territory Manager, Service Professional, Industry Expert, and Technical Sales Professional. However, the sales team subgrid only shows connections that have a connection category of Sales Team.
D365 Sales uses the Opportunity Sales Access Team template to provide access to the opportunity record to all the users connected under the Sales team connection role category. A salesperson who might not have access to a given opportunity record by their assigned security role privileges can still get access when added as a sales team member from this subgrid. This allows the sales team member users to access and work with the opportunity record on a per-record basis. When an existing sales team member is deleted from the subgrid, the access to the opportunity record is also removed.