@jeremy.koster , do you happen to remember which version of gfortran you used? I’m running into the same problem you did and followed the instructions you linked. I tried downloading the experimental gfortran for the M1 chip (Release gfortran 11-experimental-2 for ARM Big Sur (macOS 11) · fxcoudert/gfortran-for-macOS · GitHub) but am getting an error when running the Rcpp test suggesting it didn’t work:
ld: warning: directory not found for option '-L/opt/R/arm64/gfortran/lib/gcc/aarch64-apple-darwin20.2.0/11.0.0'
ld: warning: directory not found for option '-L/opt/R/arm64/gfortran/lib'
ld: library not found for -lgfortran
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make: *** [sourceCpp_2.so] Error 1