He isn’t ‘doing it for Trump’ whatever that means, this is an ongoing issue that has succeeded many administrations both Democratic and Republican and Tory and Labour, in short, it’s complicated!
The Chagos Islands are strategically important in that they play a vital role in regional and global security, which is almost certainly why the UK and the US poked their noses in in the first place, many years ago, because it was of benefit to us.
You can use this as an opportunity to bash Starmer and Lammy and this government if you want, but I would advise that you read up on the subject and try to understand the complexities of the situation. It’s not as simple as you are making out.