Does the add_regressor method on Facebook Prophet also work with categorical variables?
From my understanding Prophet is just a linear regression library that helps to analyze time series with some nice features (like holidays, Fourier transformation, etc.). So from the mathematical standpoint, the regressor must be an ordinal scaled value. The docstring also implicitly says something about it. See the keywords 'additive' and 'multiplicative'. Categorical data is neither of the two. A category is a nominal scale, which can only be counted and if it's ranked, it can be sorted.
Have a nice day.