[Assuming that the grey painted surface is the "outside", the location of the hinges would dictate that it an was inward-opening door.]
That's what I thought when I saw the original post in Freight Dogs. But I'm not so sure now though - the recently-added second photo shows an apparent flange on the right side, which suggests that the door is closed by pulling it towards you. An edge-on photo would be useful.
I stick with it being an internal door. Definitely aluminium alloy, definitely an aircraft part (I recognise the standard pitch of the MS20470 AD4 rivets
).