A few questions

[Mister Agenda]

And please tell, what about the opinion that the universe was designed by an intelligent designer/ architect/engineer doesn't make sense.?

The part where there's no more evidence for it than for a lion with goat leges.

Can you 100 % be certain of the scenario that it isn't this way?

Some people can. How certain people are one way or the other is irrelevant, certainty has little to do with what's actually the case, else you wouldn't have people equally certain of mutually exclusive things. However such certain people are in the minority hereabouts.

If you can't, you would be agnostic.

I am agnostic. An agnostic atheist. Most of the atheists here are agnostic atheists. I bet you're an agnostic theist.

Can you say for SURE that we are the cause of our existence is that the universe just HAPPENED to start with the big bang, stars formed, chemicals formed, planets etc . . . are we to give credit for our existence just to luck?

There's a certain kind of person who can think about a universe exploding and stars forming who thinks it's appropriate to put 'just' in front of such a grand conception. And is so deficient in awe as to complain there's something wrong with it if it doesn't conform to their preferences concerning probability.

And here's where we see if you're an agnostic theist: Can you say for SURE that an infinite being just HAPPENED to decide to create the universe starting with the big bang, stars forming, chemicals forming, planets, etc...are we to give credit to our existence to just luck, when presumably the creator had infinite options and picked just this one that has you in it?

Because if the universe worked in any other way than it did in the past 13.7 billion years . . . It's safe to say we wouldn't exist.

But it's not safe to say no one would exist or that the universe could have worked any other way. We have only one universe as a sample, and no evidence that 'the constants could have varied'.

So out of the infinite possibilities of what could have happened, we have a star created from a molecular cloud collapse, 4.57 billion years ago, planets got created. If even one planet out of 8, (except maybe mercury) would never have been created, earth wouldn't still be the same distance from the sun (and our position right now is perfect).

The possibilities are vast, but not necessarily infinite. It's not clear at all that the past could have unfolded differently than it did. It's certainly a possibility, and I think it's at least a bit more likely than getting the exact same result if it was somehow rewound and started over from the beginning. Still, not an established fact.

These conditions were necessary for life. Why out of the infinite number of other possibilities, like what if dark energy really didn't / doesn't exist to expand the universe with the same "force" (I can't think of a better word) it does now?

If things were different, then they would be different. Why would a being who can make universes to order need for one to be habitable in order to have us in it? An omnipotent being could have us living on the sun as easily as anywhere else. The only universe we could live in that DOESN'T require a powerful entity to explain our existence is one whose natural laws allow us to exist.

Logic, and laws dictate that there should've been multiple future possibilities. And since you proved chaos, there was no reason for things to happen as they did. And yet they have. Out of the multiple future possibilities, we HAPPENED to come to life.
Luck?

Texas sharpshooter fallacy. Shoot wildly at the side of a barn and then draw the bullseyes around the bullets that hit and proclaim yourself an amazing shootist. Everything is amazingly improbable when you work backwards from the results. How could the bullet have wound up PRECISELY in this spot if it wasn't what the shooter was aiming for? What were the odds of you being born? Your parents had to meet, one particular sperm out of millions had to fertilize one particular egg to result in you, and that means your parents had to have sex at a particular point in time to conceive you. The odds against any given Bridge hand are about six billion to one and I can deal them out all day...it's only remarkable if you know what the hand is going to be before its dealt. The odds of lots of things in advance are wildly improbable...but once they've occurred the odds that they happened are 100%.

PS- I really would love to know if there were multiverses where they work different to our universe . . . How their systems formed, if and how life evolved there and how life evolved when the properties of the multiverses were different from ours. Really exciting field!

I'm hopeful something will come of it, but there's not enough evidence supporting it yet to say I'm definitely on board.