Even people absolutely vital and critical for the business can be fired, because businesses are managed and run by imperfect humans.
One of the biggest tragedies of human enterprise is how laughably bad we are, statistically speaking, at management and leadership. I know, I've done it myself; but also seen how it is done right.
Just because you know the business will crash if you are fired, does not mean you are immune from office politics, sociopath gaming, becoming a scapegoat for a higher up who just wants to retain their bonus as they will be leaving early next year anyway, and simply because someone does not like you.
Laws will not protect you, because if they really want to get rid of you no matter how important/useful/profitable worker you are, they will manufacture the paperwork to shield themselves. You may think such paperwork is easily dismissed, but you forget: it is those exact same tactics that got them there in the first place. They've got experience in such games.
The sooner you find a different job, the better. Do not be like me, and burn yourself out and fall into depression, because you think you can "win them over" or "show them". You can't, because they are only interested in their own short-term personal gains: the hell with the company, business, and everyone else.
In the end, very few humans are actually rational and logical; most do run on pure short-term planning and instict and emotions.