I dont think this is true, and seems to be pushed as disinformation. Some are clearly fake, like the one with a man sticking a phone against his head.

In plain physics: You have to inject crumbled iron nails into someone to make a magnet stick onto you. Magnetism is a very weak force.
But we do not see magnetism at all. With magnetism the magnet would jump from the fingers onto a body.

But instead I see magnets sticking to the skin. And this can be done with anything that is adhesive in some way. You test magnetism by putting paper, tin-foil and other stuff in between the skin and the magnet. You can also use a compass.

Most vaxed people had a band aid with adhesive on their skin. But also likely adhesive disinfectant. They can also have sweaty arms due to the fever that they are having.
People could repeat it with simply some spit on the magnet. Or with oil. These magnets also stick to some meats.
In the scientific research of "Ivan the Magnetic Boy", we see how adhesive skin can stick to all kinds of metals that Ivan puts on his skin. So this phenomenon of a "sticky skin" is not uncommon.

So purely based on physics we are not seeing any evidence for injected magnetic substances.

It would also make no sense to inject magnetic stuff into people. Controlling mice with magnets only works with big machines in a laboratory.

It would be much easier to add other mRNA (or gene therapy) in the injections that would turn people into addicts or slaves.