Yes I agree, it’s true that causally connected events maintain their ordering. However, there is no sense where one can say definitively that some set of spatially separated events happened simultaneously. And as each reference frame is valid it’s impossible to say that there is a correct “present”. If two events happens at the same time in one reference frame, you can’t then declare that they happened at the same time “in reality” as that’s not valid. The events also happened at different times “in reality” in other reference frames. And in fact, the two observers could meet and discuss that the events happened at different times.
The result is that some reference frames have other frames future and past events, so to the grandparent posts point, there is a real sense in which the future exists along with the past. No reference frame gets to say what the official “future” is, so it must already exist.
My point is that, while there isn't a single universally defined future, for every observer there exist events that haven't happened yet, and no observer is ever going to communicate with some other observer and disagree about whether an event has happened yet or not. They can only disagree about the order in which events in their shared past happened.
Additionally, there are events that are in the future for any observer in any reference frame anywhere in the universe (except for those already caught beyond the event horizon of a black hole, but their future consists exclusively of the black hole so it's not that interesting to the discussion). For a simple example, present day on Earth was in the future for any observer anywhere in the universe 5 seconds after the big bang, regardless of their speed. So, there is no reason to say that present day Earth must have already existed 5 seconds after the Big Bang.
Of course, the block universe model is self-consistent, so it's possible it's correct. All I'm claiming is that an evolving universe is also consistent with relativity, though the way it evolves is more complex than a single universal arrow of time.
The result is that some reference frames have other frames future and past events, so to the grandparent posts point, there is a real sense in which the future exists along with the past. No reference frame gets to say what the official “future” is, so it must already exist.
https://en.m.wikipedia.org/wiki/Relativity_of_simultaneity