1:1 Feedback is only visible to the author of the feedback, the recipient and the Admin(s). If the manager is not one of those three listed individuals, the manager will be unable to see the 1:1 feedback.**
For example, Employee A left 1:1 feedback for Employee B. Employee B's manager will be unable to see the 1:1 feedback unless they have the Admin role.
Managers have Team visibility, but there is no 1:1 feedback tab.
Admins have Company visibility which has a tab for 1:1 feedback.
**If you have the email ON, Managers will get an email stating that their employee has received a new Feedback and the feedback is visible within the email.