The Guardian in another article explains that they are annoyed because Musk used twitter to promote his preferred candidate.
The Guardian itself used their own platform to publicly endorse Harris.
This deja-vu of childish antics is just comical in 2024
News media has always been biased and often had some form of agenda, sometimes even driven by the government.
What you used to be able to do though was acknowledge the bias and read with that lense.
What I think was true is that there was an effort of fairness and truth telling that today is far less true. Many media companies are owned by very few billionaires and they explicitly see them as propaganda.
That said, I'd always marked the Guardian as one of the remaining old schoolers. They have some weird and dangerous views, but their ownership structure gives some confidence there is an effort of fairness overall.
(I am also lost on how a foreign media company could publish a political opinion illegally in that country under US election law??)