Very sad for the United Kingdom, I think. Back in 1982 Queen Elizabeth II refused to give up the Falklands at gunpoint; in 2024 King Charles III gives up the British Indian Ocean Territory without even a shot being fired.
Queen Elizabeth II had no involvement in the decision to defend the Falklands, other than perhaps some private counsel with the then Prime Minister, just as King Charles III will have had no involvement in this decision.
Why is it sad for the UK to no longer claim as their own and occupy a small piece of land that the ICJ ruled they didn't even lawfully have sovereignty over?
The inhabitants were planters and their workers (originally slaves imported in the 1700s); no-one is native to the islands.
And the poor folks who were expelled (and their descendants) were not even consulted this time around — this is purely a deal between the United Kingdom and Mauritius, whose only relationship with the islands is that they were both lumped together under the old colonial administration.