Seems like such a simple fix though... Blur the shared photos unless you tap preview. Or unless it's coming from someone you have in your contacts. Or just not have it show the preview at all and obviously you would decline files from someone you aren't expecting to receive files from.

Or the simple fix of just not having this P2P transfer option always enabled. It should be off until you toggle it on because you and someone you are with want to transfer a file.