The latest gfortran compilers will fail to compile the legacy fortran code needed for the root-vmc code that supports geant3 simulations with root.
The fix is to add the following flags to the fortran build options:
-finit-local-zero -fno-strict-overflow -fallow-argument-mismatch -fallow-invalid-boz
ROOT Version: 6.22.06
Platform: fedora 33
Compiler: gcc/gfortran 10.2.1