We likely live in a simulation.

Assuming it’s possible to create a simulation, the odds of us being in a simulation is 50%

But if you can create one simulation, maybe you can create 1 million. Or maybe you can create nested simulations.

So even if the chance of creating a simulation is 1%, but the creation of one simulation means millions are created, the odds of us living in a simulation are above 99.99%.

Another theory is the Boltzmann Brain. Basically the idea that a brain can spontaneously appear in space:

By one calculation, a Boltzmann brain would appear as a quantum fluctuation in the vacuum after a time interval of 10¹⁰50 years.

Which means if the universe lasts forever, but has already reached a point where worlds can’t form, there’s infinite time for something as complex as a brain to suddenly spawn. Which also means it’s more likely that you don’t exist and are just a brain that will last for a nanosecond before disappearing, and none of this is real. In fact, in a universe that lasts forever, the fact you are a brain that will disappear in a nanosecond is more likely than you being a human with a real past.