Implants inside the body cannot accelerate freely. They are held in place by the surrounding tissue. A force will act on them, and this force can cause complications, but implants will not suddenly turn into projectiles.
>MRIs don't accelerate objects instantaneously.
See some of the videos below for evidence to the contrary. Large metal objects inside the room can definitely accelerate very rapidly and suddenly, and unexpectedly and has killed people.
https://www.youtube.com/shorts/2NNJrOsw8vs "Metal objects not attached to bone may not be safe"
https://www.youtube.com/watch?v=naAZVCxhEcI
https://www.youtube.com/watch?v=uDfwxoigZZk
https://www.youtube.com/watch?v=5KuzTyn45og
The only thing I strongly disagree with is the urban myth that MRIs turn implants into projectiles. I don't think that can happen. None of the videos you linked show anything of the sort.
Yes, objects can be accelerated to dangerous velocities; but only if they can move freely (eg. oxygen bottles on a cart, wheelchairs, small objects placed on a smooth surface). Objects embedded in tissue can not move freely and won't start tearing holes in your body like reverse bullets.
It can of course still be dangerous. One lethal case documented in the literature involved a metallic clamp inside the patients head. The MRI seemed to have moved or dislodged it causing cranial haemorrhaging. It killed him, but it did not shoot out of his head like a bullet.