I think the only way to find an answer is to somewhat base it on faith not just pure science.
What if the future has already happened (at least some version of it) but the past has never existed like we know it? That’s why the simulation has been used.
If the “base” universe/Earth that we live in just appeared a few dozens years ago “as is” out of nowhere then the only way to make it “real” is to actually simulate the past.
Mandela effect and predictive programming are actually anomalies in favour of multiple iterations on the simulated past.
Now the question is who benefits from this and why? The technologies from the future (which are not distinguished from magic) and antagonist - Devil/Lucifer that is not interested that we see God as the creator or maybe even furthermore to undermine God’s role or maybe even trap him in this reality.
This actually also answers the question why we don’t have a proof that God exists because someone put real huge effort to disprove it i.e. here’s a given reality, now how we came here but without God?
Apparently all efforts on this failed otherwise we would never even heard about concept of God or simulation. And it also proves that we’re indeed in “base” reality.
And because God does exist in this reality the future is not predetermined despite whatever means antagonist is using to prove otherwise.