A theory I've been writing into a fiction for a while is that Earth is just the oldest planet with life on it and Humans are the most technologically advanced species in the universe. The reason nobody has contacted us is because the rest of the universe is still basically in the caveman stage. Of course, my story is set like 1000 years in the future, after we have FTL spacecraft and start finding alien life on other worlds to know this. Also: Things don't turn out well for the aliens.
There is actually some real theories, i think kurzgesagt covered or at least mentioned it that makes a mathematical case for us to still be in the very early stage where advanced complex life can possibly form.
Also, if you compare the age of the universe right now to how long it will be until heat death, we are absurdly early. We're in the first 0.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000001% of the universe's lifespan.
Oh for sure. My own hypothesis or twists on them generally come from actual things I've heard or read about, and I do watch a lot of Kurzgesagt. Even completely baseless ones, like Creationism, has some interesting ideas perfect for fiction to explore.
Thing is, the universe is really really really fucking big and old. There might have been a million other super advanced societies throughout the universe space and throughout the universe life, but the chances of us knowing about them would still be negligible.
There are tens of billions of planets just in the milky way, most of them probably at least 5 billion years old. And there are hundreds of billions of galaxies in the universe, if not trillions. The nearest one is 25,000 light years away. Do the math.
The chances of life existing elsewhere are pretty much 100%. The chances of us ever knowing about it are pretty much 0%.
NOPE! It's a cyberpunk dystopia. We're spreading crapitalism across the universe, like a plague!
The other thing I'm trying to do with this is have non-human primary character heroes in a world where humans exist, because I've never seen that in other fiction before. Avatar (the James Cameron film) was close; but the protagonist is still technically a human.
Sounds like a good story. A lot of SF has a forerunner civilization concept, but I can only think of a couple that present anything about their early stages.
One of my DMs ran a campaign in his world, specifically to have a story because he had been world building for 6 years at that point. Might be something to consider, obviously you'd probably need a system other than D&D, but there are loads of Sci Fi systems out there that could probably be adapted to your world.
That's also how the first Dragonlance novels were written.