Very good questions, André, but I see I need to focus first on one important aspect.

Let's go back to the clock sent into space, coming back to Earth with a different time on its display.

This is where we must answer the following question:

Did...

A/ time dilate, or

B/ did matter's behavior of the clock change?

Like a measure tape correctly measuring how tall we are, no one in their right mind would say that the measure tape was involved with how tall we ended becoming, right?

A/ The measure tape shrunk (so we grew)

B/ We grew and the measure tape shows that

Everyone would say that B is the answer, and that A is ‘wagging the dog’.

Back to the clock showing us the changed time on its display:

A/ Time dilated, or

B/ Matter (the clock) changed its behavior

Do you see what I am saying? Explaining the specific behaviors of motion that Newton could not explain, but that Einstein did explain, should still be based on matter's reality of some kind, right? It is strange to call it out as Spacetime.

The Fourth Motion name replaces therefore the Spacetime name. In other words, I work with the Fourth Motion to explain the specific movements of matter that Newton could not explain, and that Einstein explained with the term Spacetime. I claim that Spacetime is a horrible misnomer, because specific movements of matter must be explained in a fashion that fits not with spacetime but with matter.

So, I am saying that Einstein hung his extremely smart hat on the wrong thing. Einstein was truly correct, but not in the naming convention.

So far, everything is fine. Yet next, physicists started to invert what Einstein delivered; they started wagging the dog instead of having the dog wag its tail. They focused on the wrong part.

Do see that no matter if we pick A or B that Einstein was correct. Either way.

It is a superficial distinction therefore, but in one version we understand reality in an inverted way from the other version.

Einstein expressed the distinction well. But the scientists following Einstein put the wrong thing in top position. Most likely, Einstein understood that there was no good scientific way to explain the difference.

For specific subject matters, Einstein objected to other physicists inverting his Spacetime. In general, he did not engage into these specifics, because either way he was correct.

-- -- --

So, I do not use Spacetime. Rather, I state that (most of) the special behaviors that are explained by Spacetime are explained instead by the Fourth Motion. I place the special behaviors of matter on a special circumstance for matter.

Let me leave it at this, André, while I don't mind answering your questions, I'd like to see if you got this very small-major distinction that inverts the idea we have about the universe.