This is my designed MTG Commander Deckbox.
You can fit up to more than 120 Card with sleeves and some dices as showen in the pictures.
The magnets i used are 20mm x 6mm x 1,5mm.
https://www.amazon.de/First4magnets-F330-10-N42-Neodym-Magneten-Packung/dp/B00382J9UO/ref=sr_1_2?crid=39P46JIWQXYDN&keywords=20x6x1.5mm%2Bmagnet&qid=1706113359&sprefix=magnet%2B20x6%2Caps%2C78&sr=8-2&th=1
The hardcover showcase (toploader) card is 3"x 4".
https://www.amazon.de/AMIGO-81222-Toploader-regular-Fix/dp/B004KHV24W/ref=sr_1_6?__mk_de_DE=%C3%85M%C3%85%C5%BD%C3%95%C3%91&crid=72T1XYJOU93D&keywords=top+loader&qid=1706113465&sprefix=top+loade%2Caps%2C89&sr=8-6