That's not even the story of dark matter and dark energy. Dark matter was theorized first I'm pretty sure because the expected motion of galaxies is completely different from the actual observed motion, so the theory is that they weren't detecting all of the matter that's in the galaxy properly, because the observed motion implies that there is more matter in the galaxy than they can detect. So that's where the theory came from. There's some other evidence of dark matter like when galaxies collide there's evidence that something additional collided that nobody can see besides means of analyzing the gravity, but the record of dark matter is mostly minimal.
Dark energy is very similar to dark matter and it's not the same thing as anti-gravity, it's much more similar to dark matter.
There's no guarantee either are real or fully-understood, but it's very likely that they actually are real and are difficult to study.
The big bang theory has much more evidence than the prior two topics, to the point where it's barely a theory but more of a factual model. And the "singularity" is not understood yet, because science is not in the bullshit business and they don't just make up answers when they don't know the answer. So for now the earliest stages of the big bang are very mysterious still, but they have definitively proven that the universe is currently expanding and that if you go backwards in time, it was (intuitively), compressing. Until the point it can't be studied anymore which was about 13.7 billion years ago.
