No, Facebook will not send them a notification saying "John Doe has unblocked you."
It feels like it should be simple. Just a reversal, right? Wrong. Unblocking someone on Facebook is not simply "undoing" a block. It is a deliberate act of digital resurrection, and understanding what actually happens when you click that button can save you from a world of confusion, awkwardness, and unexpected social dynamics. what happens when you unblock someone on fb
They will probably find out eventually, but not via an alert. No, Facebook will not send them a notification
If someone tagged you in a photo or post before you blocked them, and you unblock them later... nothing happens. That tag is dead. Unblocking someone on Facebook is not simply "undoing"
Unblocking someone is a gesture. It says, "I am no longer actively avoiding you." But it is not an apology, an olive branch, or an invitation.