A simple deck box, with room for 100 double sleeved cards, and magnetic latching.

The key feature though is the quick swappable and customisable badges, allowing the deck boxes to be customised to the game or deck that you are playing. The badges are available here: https://www.prusaprinters.org/prints/122300-customisable-magnets-for-deck-boxes-mtg

It needs eight 10x3mm magnets.