Not all matters can be objective. It is impossible for all things to be objective. Many things people see as objective are subjective. Much or our world is our conceptualization.
You cannot objectively assert that. According to the law of the excluded middle, all propositions are P or !P. That means all opinions are either true or false.
Objective and subjective things can both be true or false. It can be true that I hold an opinion. "I think burgers taste good" is a subjective statement, and a true statement.
