As an admin, you can decide whether or not you want students to complete feedback after a session (for both appointments and sections). From the admin panel, you will either Enable or Disable this feature. Moreover, you can decide how long after the session the student is allowed to submit their feedback. For example, if this setting was set for 2 days after, the student would have two days to complete the feedback before it is hidden from their learn screen.
Note that adjusting these settings will apply to sessions that have already happened and future sessions. So, if you disable student feedback, or make the feedback submission date length shorter, past "feedback needed" sessions will be hidden from the student's learn screen.