Welcome to the Forum @Gabriel_Budemberg and thank you for reaching out!
Regarding to your question Admins can see the list of members of all Teams in the Organization but they are not able to see the content of a team they are not members of.
When you add a colleague to your Team, he/she will have access to all Team Conversations and public projects within that Team. You can read more about it in the following guide article: Team permissions
What might be happening here is that there are private projects within your Team that your Manager is not a member of. You just need to add him as a member of these Projects.
I hope this helps but please don’t hesitate to reach out if you need further assistance!
Have a great day!