there are many different theories with different ways of answering this question
'presentism' is the view that neither the future nor the past exist; that the matter of the universe only exists in the present moment, memories and anticipations are just illusory projections, from the present moment
'four dimensionalism' refers to the view that the
past, present and future are all 'equally real', and that (tenselessly) there exist dinosaurs, people and (if there will be such things) cities on Mars. These things don't exist now but they do exist, with the analogy often being that, if I am in London, New York doesn't exist here even though it does exist.
so is the future real or unreal?
When arguing that a reality necessarily exist, inevitably what is called "past" can in human perception only be as real as the individual perception thereof. For the same reason what is called "present" in human perception inevitably follows that same rule and so does what is called "future".
From which follows that "future" is and always shall be out of reach because impossible to be perceived before it becomes the present, and if it is the present it becomes the past at the same moment.
Hence when arguing that a reality necessarily exists and needs to keep existing for that reason, "future" is all it can be.
salaam.