This is a photo holder for the Fujifilm Instax Mini format (46x62 mm).
The holder has a round pocket on the back that allows inserting a ferrite magnet to attach the item on a metallic surface.
The ferrite element should fit tight, but I use a bit of hot glue to be sure.
I print it with supports (it worked well with the “organic” supports).
The author marked this model as their own original creation.