Metal business cards come in various colors, matte or glossy, as well as various thicknesses.
Your design (which can be designed by me if you’d like) would always be silver, since that is the color of the metal after the laser has etched away the surface color.
QR-codes can be added, but in general it’s best to avoid very fine detail or details too close to the edge of the cards, since getting the cards aligned properly with the laser is something that may be off by a few millimeters.
I have not tried making double-sided cards in the past, but I don’t see why it wouldn’t be possible.
I cannot produce these in mass quantities, and making any at all is dependent on the laser-cutter at the local makerspace being in working order.