There are also all the laws the monarch / monarch’s lawyers interfered with e.g. police can’t enter Sandringham Estate without an invite, leaseholders on the Duchy of Cornwall are excluded from buying their freehold
The thing about Britain's constitutional arrangements is that there are many things which 'can't' be done, which it turns out simply 'aren't' done.
What is sovereign immunity?
Sovereign immunity is a centuries-old doctrine dictating that the monarch cannot be prosecuted or subject to civil legal action under the law. Its origin lies in doctrine and convention, rather than statute, and there is no law setting out the rules underpinning the concept.
It stems partly from the medieval concept that the monarch is the source of justice, and can therefore do no wrong. It also relies on an argument that because the courts belong to the Queen she cannot be compelled to appear in them, since she would, in effect, be prosecuting herself.
Since at least 1800, the monarch has also had a legally distinct private persona, created to allow them to have independent wealth and property that could be inherited by their children. However, the lines between the two are somewhat blurred, and sovereign immunity has typically been interpreted to apply to both the public and private identities of the monarch.
We take it for granted now, but it was a beginning of constitutional order - king and government should follow certain laws and rules for how to run the country. And the UK is after all a constitutional monarchy, no longer at mercy to the whims of an autocratic monarch.
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.