[chippiewill]

That's not true these days, the King doesn't actually have those powers themselves - even on paper.

The power actually sits with "The Crown" not the King personally. "The Crown" is a legal entity that is represented by the King but not actually wielded by them. The Prime Minister advises the King on use of those powers which is what actually creates the legal conditions where they're effected by The Crown.

A good example of this is when Boris Johnson unlawfully prorogued parliament in 2019. The Supreme Court ruled that his advice to Queen Elizabeth to prorogue parliament was unlawful, and therefore "The Crown" could not have prorogued parliament and parliament was never prorogued. This would not be the case if it were a power that the Queen exercised themselves.

If the King were to attempt to dissolve parliament without advice from the PM by generating an order in council and sending it to Parliament then the supreme court would simply rule that he hadn't dissolved parliament.