What if God created the universe but the Buddha just discovered how it works?

If you're talking about a God which is not a being but the cause of all causes then yes that God is the same as our True Nature or Buddha Nature as Buddha called it.

If you're talking about a God which created worlds, galaxies, etc. then that is simply just a God in the form realm or the higher Desire realm heaven. (See Thirty-One Planes of Existence.)

If you're talking about one specific being created this entire universe (and all multiverses) including its countless solar systems within countless galaxies... then (1) you need to look at some astronomy videos and (2) the The Buddha specifically says that specific Gods (from the Form and Desire realm heavens) that delight in creation created particular galaxies/places and no one God created every single thing.

He also says that excessive speculation will only waste your time and distract from the actual issue: unhappiness and being trapped in birth-and-death.

Is it more important to be find True Happiness (free of conditions like having physical pleasure, the right relationship, enough money, etc.) and be able to decide where you go in the universe or is it more important to spend your life intellectually understand the origin of the universe?

The Buddha emphasized the former and said that the latter would take too long to explain (although he did a good job with the 31 Planes of Existence).

It's just as if a man were wounded with an arrow thickly smeared with poison. His friends & companions, kinsmen & relatives would provide him with a surgeon, and the man would say, 'I won't have this arrow removed until I know whether the man who wounded me was a noble warrior, a priest, a merchant, or a worker.' He would say, 'I won't have this arrow removed until I know the given name & clan name of the man who wounded me... until I know whether he was tall, medium, or short... until I know whether he was dark, ruddy-brown, or golden-colored... until I know his home village, town, or city... until I know whether the bow with which I was wounded was a long bow or a crossbow... until I know whether the bowstring with which I was wounded was fiber, bamboo threads, sinew, hemp, or bark... until I know whether the shaft with which I was wounded was wild or cultivated... until I know whether the feathers of the shaft with which I was wounded were those of a vulture, a stork, a hawk, a peac**k, or another bird... until I know whether the shaft with which I was wounded was bound with the sinew of an ox, a water buffalo, a langur, or a monkey.' He would say, 'I won't have this arrow removed until I know whether the shaft with which I was wounded was that of a common arrow, a curved arrow, a barbed, a calf-toothed, or an oleander arrow.' The man would die and those things would still remain unknown to him. —Cula-Malunkyovada Sutta: The Shorter Instructions to Malunkya" (MN 63), Majjhima Nikaya

In a way there ultimately is no Sims. The Buddha taught how one can see past the simulations that we make up and assume are real. This is how we transcend the assumptions we have about suffering and find true peace and happiness :)

What if God created the universe but the Buddha just discovered how it works?

Well that's great because after The Buddha discovered how it works he shared with the rest of us how to be free from suffering.

Note: He didn't share with us How it All works and who created the universe. You know why? Because when he was sitting there trying to find the answer to that question he realized oh my god this is going on forever and ever, thats when he realised he had bigger fishes to fry. Like "Suffering and the Cessation of suffering".

In the Sutta Cula-Malunkyovada Suttahere's an explanation of a man who got shot by an arrow and instead of getting help immediately he wanted to know who shot him,what weapon,what clan the shooter came form etc.When he should really be treating the wound.The wound is suffering and we should be treating it instead of trying to find if There's a God or when this universe was created sort of questions.Because it distracting us from the the real problem,that of suffering.