I am using 8x Neodym 5mm x 1mm circle magnets. It is a really tight fit so you might have to use some force to put them in. Don't forget to glue them in aswell. When you are using thicker glue you can also use only 1 magnet for each hole.

You can change infill to 50% if you want to make sure it doesn't break when you insert the magnets.

The magnets I am using: https://www.amazon.de/gp/product/B08F7DKGQR/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1