Hi Bohdan,
Opportunity Stakeholders sub-grid is irrelevant to N:1 relationship of Opportunity and Contact.
Let me show another specific example to help you understand:(with default sub-grid settings)
1. There is an opportunity called "Printers", its contact and stakeholder are both Adrian Dumitrascu.

2. When viewing Adrian Dumitrascu profile, we can see the opportunity is available to his recent opportunities.

3. Back to the opportunity, we add Clofly Mao as its another stakeholder, then the opportunity has two contacts.
However, they are associated with connection, we can expand its related connections in associated view.


4. Open Clofly in form, we can see that Clofly has its own opportunity, while "Printers" is not available to the sub-grid.

Similarly, the associated "Printers" of Clofly can be found in associated connections view:

5. Opportunity "Dynamics Marketing app" is owned by Clofly,

while "Printers" is owned by Adrian Dumitrascu.
In other word, there is no direct relation between contact Clofly and opportunity "Printers", but "Printers" can still be associated with Clofly through connection.

Regards,
Clofly