It means “that being said”. You can (or even should…) replace it by “Cela dit” or “cela étant”, or even “quoi qu’il en soit”. But note that this is very much a colloquial use of “après”, you could hear it in some informal conversations, but it is something you should avoid in written or formal speech. I would not be surprised some people may even frown upon this usage and regard it as “bad” French. I have just looked in a couple of online dictionaries, and they don’t mention this specific meaning for “après”.