Just to clarify. The King of the UK is above criminal law. The monarch of the UK cannot be arrested or charged with an offence, or be personally involved in criminal proceedings.
That is similar to the immunity given to the sitting US President. What is different is that monarch is not really expected to obey the law either. For example, the Prime Minister was fined for illegally not wearing a seatbelt. If the king didn’t wear a seatbelt, it would not be a big deal - the royal family freely ignore traffic laws (and more serious laws) without consequences. Queen Elizabeth did agree to start paying taxes, but there was never any suggestion that she be compelled to pay taxes, merely that it would be the right thing to do.
That is similar to the immunity given to the sitting US President. What is different is that monarch is not really expected to obey the law either. For example, the Prime Minister was fined for illegally not wearing a seatbelt. If the king didn’t wear a seatbelt, it would not be a big deal - the royal family freely ignore traffic laws (and more serious laws) without consequences. Queen Elizabeth did agree to start paying taxes, but there was never any suggestion that she be compelled to pay taxes, merely that it would be the right thing to do.