Opportunity 1 was created by User 1 whose Role is 'Account Manager' and whose profile is 'Standard User'

When I do an API call using User 2 credentials, to get all the opportunities, Opportunity 1 is not returned in the list.
User 2 Role is 'Developer' and the Profile is 'System Administrator.

Per your documentation, I have changed the Sharing setting of OPPORTUNITY to allow Developers to see all the opportunities created by an Account Manager.
But I still cannot see it.

Opportunity 1 was created by User 1 whose Role is 'Account Manager' and whose profile is 'Standard User'

When I do an API call using User 2 credentials, to get all the opportunities, Opportunity 1 is not returned in the list.
User 2 Role is 'Developer' and the Profile is 'System Administrator.

Per your documentation, I have changed the Sharing setting of OPPORTUNITY to allow Developers to see all the opportunities created by an Account Manager.
But I still cannot see it.