It should be clear that the word "omniscience" means different things to different people.
The following sums it up nicely
"The commentarial view is that all knowable things are potentially accessible to [the Buddha's understanding, panna], but that they are not all simultaneously accessible." This then leads to the question of what is meant by a knowable thing, which, as Ven. Dhammanando explains, "is an important qualification, for nowhere is it asserted that all things are knowable things." And so the Buddha's "omniscience" as the commentators understand it, is far from being the Allah-like or Jehovah-like omniscience that some Mahayana Buddhists posit.
Again, I wish you good luck with this concept-simplification, in endless hardship what is total and beyond concepts, if you prefer it. Moreover every concept, no matter if omniscience or other, always means different things to different people.
the details of future events
Moreover details of future events are just imaginary nature because there is no "fatum" or "sin" in Buddhism as you know, unlike Islam or Christianity. Again, if such things will be possible to know they would be only by all-knowing buddhas "out there", so out of our reach "out here". One more object-side perspective paradox. One more view of eternalism according to Madhyamaka.