BRUSSELS—The European Union set out a formal strategy on Thursday to boost its presence in the Indo-Pacific and counter China’s rising power, pledging to seek a trade deal with Taiwan and to deploy more ships to keep open sea routes. The EU’s foreign policy chief Josep Borrell insisted the strategy was also open to China, particularly in areas such as climate change, but diplomats told Reuters that deeper ties with India, Japan, Australia, and Taiwan were aimed at limiting Beijing’s power. Borrell also said Wednesday’s agreement between the United States, Australia, and Britain to establish a security partnership for the Indo-Pacific, in which the EU was not consulted, showed the need for a more assertive foreign policy. He said the EU was eager to work with Britain on security but that London had shown no interest since it left the bloc, expressing regret that Australia had canceled a $40 billion …