Help using RStan - stdlib.h file not found

Does the error message occur specifically with hBayesDM, or does it occur with anything involving rstan? Are you able to run this: example(stan_model, package = "rstan", run.dontrun = TRUE)?

When I searched through Discourse with “Mac M2”, I found quite a few threads with error messages similar to yours, e.g. this thread may be useful.