These have existed for a while [1]. I've been using one to make sure that my business and personal cards aren't both charged in public transport
NFC uses magnetic antennas/coupling meaning that shielding from one side is enough to block signal.
My solution is to laminate strip of aluminium foil in card form factor.
As well as testing an active jammer that's for sale https://www.youtube.com/watch?v=rnOuEFR6qoM