You can't prove a negative.

That principle doesn't apply here, because you can use simple language to turn the words around, and then you have a positive, while the task of proving it remains the same.

Specifically: when you say you can't prove that we don't live in a simulation, then it is the same as saying you can't prove that we do live in reality.

But "we do live in reality" is a positive. Now the words are different, but the task is the same: prove that we live in reality.