0- Suppose by absurd that we are in a simulation. 1- We are equally likely to be in one of the many simulations. 2- The vast majority of simulations are simple [see paper to understand why this is reasonable]. 3- Therefore, we are very likely to be in a simple simulation. 4- Therefore, we should not expect to observe much complexity. 5- But we do observe complexity, therefore we are very unlikely to be a simulation.
For an argument against the sim hypothesis see https://lorenzopieri.com/sim_hypothesis/ or the full article https://philpapers.org/rec/PIETSA-6 (The Simplicity Assumption and Some Implications of the Simulation Argument for our Civilization).
In a nutshell:
0- Suppose by absurd that we are in a simulation.
1- We are equally likely to be in one of the many simulations.
2- The vast majority of simulations are simple [see paper to understand why this is reasonable].
3- Therefore, we are very likely to be in a simple simulation.
4- Therefore, we should not expect to observe much complexity.
5- But we do observe complexity, therefore we are very unlikely to be a simulation.