Hi - these types of questions are really hard to answer from a distance, particularly without access to your Salesforce instance. I genuinely suggest you work with Marketo Support on that - they will need to get lots more information on your sync setup and will be able to work through different sync scenarios with you.
Thank you for your reply, I found a solution, to share it with you!
The issue was the visibility of our technical user who does sync between salesforce and marketo.
If the technical user in Salesforce doesn't see the record opportunity, it will not synced with Marketo.