I bought a bunch of magnets ages ago and have started embedding them in projects, these use some tiny 3mm diameter discs that are 2mm thick, and the voron spec magnets I had leftover, 6mm diameter discs 3mm thick.

More of a proof of concept, I keep these in onshape and then use them to go from there for containers.

The grid also has embedded 3mm magnets, it is 7x3 which fitted my shelf depth nicely, and my print bed.  Doesn't fully prevent slipping, but gives it enough purchase on the shelf to stay put with most of the holes populated.

Slice and use a colour change (on your prusa will trigger colour change, but on my klipper macros triggers a pause for a manual filament change or embedding of anything in to the print).

If you're printing in the go to 0.2mm layer height as I usually do, set your first layer to 0.2mm as well rather than a thicker one, that will make the slicer give it two thin layers under the magnets rather than one if your first layer is thicker.  It will still work, however 2 layers is probably going to be better than 1 under a magnet.