This is my take on a magnetic knife board.

I've created a parametric model, so you can generate an stl with holes that fit the magnets that you have available or can more easily source. I had small magnets (15x6mm), and admittedly those are not ideal, but will work if you stack a few of them. I used some hot glue to keep the magnets in place, but you can also use cyanoacrylate or epoxy glues.

I recommend cylindrical neodymium magnets, probably 20mmØ or bigger will work well. The maximum size magnets that the model will theoretically work with are 32mmØ, as these seem to be widely available online, but I have not tested them.

Both parts assemble with three M3 screws (15mm at least).

I printed the base with 20% infill and it would've probably benefited from a little bit more weight. I would try solid infill if I had to print it again. These large prints benefit from a wider nozzle; I printed mine with a 0.8mm nozzle at 0.4mm layer height and they look amazing.

I've generated two stl files for the body: one with 15x6mm cubic holes, and one with 32mmØ cylindrical holes. Let me know if this model works for you or if you have a suggestion for any modification.