Gridfinity is an open-source grid storage system for your workshop, desktop ... The Gridfinity designs were first released in the video Gridfinity: Your Ultimate Modular Workshop is FREE! as a framework for the community to extend.
This page discusses the polarity of magnets in Gridfinity elements.
Zack Freedman has created a 1x1 base plate as a reference. He suggests that anyone wishing to create compatible elements should send him their magnets by post, with a self-addressed stamped envelope. This isn't exactly ideal, especially for those outside the US. After reading several threads on the subject and realizing that everyone did things a little differently, I opted for the solution that seemed most natural to me and which is mentioned in the very question of the Reddit thread:
I finally installed my first magnets this morning. I went with north pole up. Very Eurocentric of me, I know.
The north pole of the magnets therefore faces upwards:
Then it's time to find out where the north and south poles are on the magnets. You can find more or less effective techniques online. After some research, I finally found a simple and effective solution: I use the Pole Detector app on my phone: