Would not all the near infinite configurations of matter/energy, galaxies, stars planets, etc - the sheer mass and gravity of a block universe - be detectable?
A block universe is just a single universe with (at least) four dimensions - three spatial, and one of time - wherein time is dependent on the relative motion of the observer, as described by Relativity.
In Einstein's universe, observers moving at different rates agree on the speed of light, but disagree about the timing, and even the sequence, of events they observe.
This apparent paradox - that events can occur in different orders for different observers - can be resolved by discarding the concept of a single and universal 'now'; 'Now' ceases to be special or different from 'then', as your 'now' might be in my past, or my future.
The way Einstein envisaged this was to to model spacetime as an unchanging four dimensional 'block', through which each observer's 'now' constitutes a slice that moves through the time dimension at an angle that is dependent on their motion.
The 'sheer mass and gravity' of this block universe is the observation that (General) Relativity seeks to explain - by invoking a block universe Einstein was able to correctly model the observed motions of objects in space, where Newton's model has inaccuracies.
So the answer to your question is 'Yes, and it is'. At least according to Einstein.
The absolute nature of the speed of light (ie that it is the same for all observers) implies that events in your future are, from the perspective of some hypothetical observers, events in their past
and vice versa.
This is, of course, incompatible with the idea that the future is not yet fixed, but the past is immutable; Einstein's block universe model resolves that by making the future as immutable as the past, because
for some observers what you call 'the future' has already happened.