If you're starting out on statistical rethinking, be sure to check out recoded [0]: a reimplementation of statistical rethinkings exercises using tidyverse, ggplot and brms instead of McElreath's own package. These tools are standard and well worth learning on their own, and they're also more documented than the package made by McElreath.

[0] https://bookdown.org/ajkurz/Statistical_Rethinking_recoded/