It is not a well understood process I am actually shocked that @ChefDong was able to provide you a sourced scholarly article, so cudos to him for that! Long story short plants seem to love being exposed to relatively strong magnetic fields, but 99% of the time only the south pole, I have done some homemade science on this myself over the last few years. Basically put a Neodymium-iron-boron magnet at the bottom of a plant pot south side up and enjoy plant yields of at least 10% +, but it is not just the yields but the quality of the plant and the fruit or veg you are growing. Exposure to north pole fields can actually lower acidity but that's about the only difference you don't get the improved plant health. Where this concept starts to break down at least in a commercial sense is that you cannot just have a south pole in isolation so put 10 plants together with magnets in each and the effect starts to cancel out, so there is a sweet spot and I have seen some pretty advanced planter designs to try and guide the fields to optimize the effect, but nothing that's commercially available to order. Welcome to another rabbit hole XD