"The future" and "the past" have very useful and well defined meanings in SR. The key insight is that they are only meaningful locally, not at the level of the entire universe as it is assumed in Newtonian mechanics.

Every possible observer has a clear view of their own past and their own future. As long as two observers are a long distance from each other, they may disagree on the order in which events that happen far away from each of them happen.

But, they will never disagree on the order in which events that are close to either of them happened. And, if they ever meet, they will have a shared notion of what is in the past and what is in the future compared to the moment of their meeting (that is, any event that is in the future compared to their meeting for one of them is also in the future after their meeting for the other).