[R-SIG-Mac] Catalina and gfortran

[Erich Subscriptions]

I am trying to produce a n R environment on clean new Catalina installation (in a VM).
The R binary installer and RStudio work.
Then, I installed clang7, and that seems to work also.
gfortran, however, is a problem.
The 4.2.3 version (still in the tools folder on CRAN) is 32bit only,
so it does not work on Catalina.
6.1 from https://github.com/fxcoudert/gfortran-for-macOS/
cannot be installed, the installer tells that it is incompatible with this version of macOS.

Is there a workaround? Can I find a version of gfortran which will compile
packages containing Fortran code?
(I stumbled on classInt).

I also tried gcc using 7 from homebrew, but could not get it to run either.