When you unfriend someone on Facebook, they are not notified by the platform. Facebook's official policy is that the person you unfriend will not receive any notification indicating that you've removed them from your friends list.
However, they might realize they've been unfriended indirectly through changes in their experience, such as no longer seeing your posts in their news feed, being unable to view your profile fully, or noticing they can't send you messages if your privacy settings restrict communication with non-friends.
In summary, Facebook does not send a notification when you unfriend someone, but there are signs they may notice without an alert from the platform.
