Did the past occur or is it occurring relatively ... ?
"it follows from the relativity of simultaneity that there is no fact of the matter as to what is present"
Does simultaneity relate to presentism? For sure at different locations what is observed to be simultaneous differs, but that does not affect the present moment. The present moment does not have to be defined as having the same observed events happening simultaneously. And what could anything other than the present moment even be? Different present moments together? That doesn't make sense.
Regions of spacetime may be unobservable, but that does not mean they drift apart temporally into variations of the present. That would be a completely unnecessary and absurd complication.
So the answer to the above question is: the past occurs both absolutely and relatively to a varying degree depending on one's speed of movement through space. There are no places where one person's past is in another's future. They are all in the past of the present moment.
This has no bearing on the block model, which shows a real trajectory through time. Only one time slice is the present moment. Presentism may deny the reality of the past in a manner of speaking, but that does not stop that singular time slice in the block model being the present moment. Presentism and eternalise are not at odds in this respect.
the Moving Spotlight Theory is an example of an eternalist A-theory
that subscribes to the dynamic thesis. ... Spotlighters think instead
that there is a spacetime manifold, but one particular region of the
manifold is objectively distinguished — the present.
Stanford Encyclopedia of Philosophy The Moving Spotlight Theory
Fragmentalists (see Fine 2005) think that there is a spacetime
manifold but that every point in the manifold has its own type of
objective presentness, which defines a past and future relative to the
Fine's dismissal of the present appears to rest on special relativity's view on simultaneity, but as discussed, just because different observers do not agree on what is observed as simultaneous does not mean they are not in the same present.