How can we investigate the error / noise term.

Dear all,

I noticed that Prophet uses a decomposable time series model, which includes a trend, saisonality, holiday factors and whatever additional regressor, you want to use.
But there is (of course) also a noise term. So is this noise term stochastic oder determinstic? How is the error term calculated? Can I visualize or calculate the error term in my model by myself?

I couldn't find some information about this part of the model and hope you can help me at this point.

Best regards and thank you!