The electromagnetic force is a type of physical interaction that occurs between electrically charged particles. Electromagnetism is different from gravity. Both phenomena are real but have different characteristics.
Flat-Earthers refuse to accept gravity, and some of them use electromagnetism in place of gravity to explain the various phenomena that are explained by gravity. In reality, electromagnetism has different characteristic from gravity, and cannot explain the various phenomena that are explained by gravity.
The magnitude of the force of gravity depends on the masses. On the other hand, the electromagnetic force depends on electric charges.
Gravity is very weak. Gravity requires the entire mass of Earth to accelerate an object at 9.8 m/s². A small magnet can easily produce an electromagnetic force far greater than its weight.
Electromagnetism can affect different objects differently. However, gravity affects everything the same; only the amount of mass and the distance between them count.
Electromagnetism can be shielded, or in other words, it can be covered in such a way that the electromagnetic force cannot penetrate a barrier. On the other hand, it is impossible to shield gravity.
These differences between gravity & electromagnetism can be used to demonstrate that these assumptions invented by flat-Earthers are incorrect. We can easily show that gravity cannot be shielded, and with everything else kept the same, gravity affects different materials with the same amount of effect.