See the answer below
Explanation/Reference:
Explanation: All users automatically follow each other.

Opportunity contact roles allow you to track ROI for contacts that are key stakeholders for opportunities. You need to customize the contact role field and add the related list to the opportunity page layout.
References: https://help.salesforce.com/s/articleView?id=sf.opportunity_contact_roles.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.customize_opportunity_contact_role.htm&type=5

Section: Volume G