How can one change their nature to become beloved while maintaining frankness and intervening in defense of the truth? And does people's hidden dislike imply a lack of God's love?

If you are a benevolent person who loves people, is sincere in your friendships, and fears God in your work, then you will not be among those whom God dislikes. You should also leave aside matters of others that do not concern you, as there is no necessity for them in your religion or your worldly life, nor do they benefit in gaining God's pleasure. This does not preclude enjoining good, forbidding evil, and reconciling between people, even if it causes some of them to dislike you. For the Prophet, peace and blessings be upon him, said: "Whoever seeks God's pleasure by the displeasure of people, God will suffice him concerning people. And whoever seeks the pleasure of people by God's displeasure, God will entrust him to people."