PS: If you think the British gov is authoritarian.. well, you might not know what the term means and/or anything about the spectrum of governments operating today or in the past.
The British government is certainly not as authoritarian as those in China or Russia, but that doesn’t change the fact that it’s still terrible and restricts people’s rights. For example, you can be detained for as long as they want if you refuse to unlock your encrypted device.
Supose you live in USA, your chickens have a list of laws, those laws apply to USA. If you try to sell those chickens in UK or Europe you'll find that your company will not be allowed to operate, and if you continue someone will go to jail.
Maybe digital products have an easy way out, but apple is not digital and they may need to find a way to comply.
We don't want it the other way around; companies placed outside the borders doing and selling whatever they want without a care. So we end up in a negotiation.
Apple choose to maliciously comply; subtly revealing the TCN, giving all UK users notices about what their government demanded of them to encourage public outrage, and push on the correct parts of the UK government that has their interest in mind.
They can do both of things. There's no law against leaving a country for not respecting human rights like privacy and encryption.