Thank you, @wmutschl! I merely followed the subset of instructions in the second link you shared (for compiling Dynare from source for macOS) under the heading “Compile and install the X-13ARIMA-SEATS Seasonal Adjustment Program” and no changes to the PATH variable were needed, the example mod file worked just fine. I think my setup simply lacked x13as, since it was not included in the Homebrew package and not mentioned on the quick start page.