This is a tray case for a keyboard you might receive as part of a "Mystery PCB" order from clawboards.xyz. Clawboard's minivan was an experimental break-apart keyboard with independent control for the main key cluster, the numpad and navigation clusters, and the f-key row. As you might imagine, it didn't take off, so now it's being sold at a greatly reduced price as part of a gimmicky way to get rid of the inventory.
You can buy a superior and similar keyboard, "the coupe," from the same source. However, that keyboard won't fit this case, because the controller and cable entry are located differently on that board. Because of this, the .3mf isn't going to be very useful, but you can have the .f3d as well, and maybe you can adapt this case to something more standard.