Here is my best shot of making a replica of the Gameboy/Gameboy Color cartridges and turning them into magnets. I even tried to copy their pinout. They should be about the same size as their real counterparts. They have a hole for an 8mmx2mm magnet and should be press-fit; you can always add super glue if you want to be safe. Also, the center cut-out is 43mmx39mm, so feel free to make your own. Here is a link to the ones that I created: https://drive.google.com/file/d/1oX703tbJYDUlGyL3vGm9mfA621f-N6Js/view?usp=sharing
Let me know if you have any trouble accessing it or if there is a better way to attach it. Also, feel free to message me if you want to know any of the filament brands/colors I used. No supports are needed; also, if you lay flat, I recommend using ironing for a better finish.
I got this idea from a random reel from a short on YouTube and took my shot at making them.