Versions of this idea have been discussed all the way back to antiquity. The modern interpretation was popularised by Oxford University philosopher Nick Bostrom in 2003 and has since been expanded by many others, including MIT professor Rizwan Virk.
The simulation argument supposes that computer power will continue to increase to the point where it is possible to model enough of reality to mimic everything that we are currently able to perceive and measure. This needn’t be as complex as a complete model of the Universe. The stars in the sky could be simulated just as points of light, with no other features until we point a telescope at one.
If we assume such simulations are possible, then it seems inevitable that there will be more than one; and thus, statistically, we are more likely to be in one of the simulations than the single ‘true’ reality.
Even if we one day manage to build such a simulation, that doesn’t rule out the possibility that we are nevertheless in a simulation of our own. In fact, we could be in a simulation within a simulation, within a simulation that extends endlessly above us. But all any of us will ever know is limited to what we can directly perceive, and whether our ‘reality’ is more or less real than some other version we can imagine is ultimately a fairly meaningless question.