@Certik has stated that the Fortran community should try to understand why important Fortran codes are migrated to C++. There are two versions of NEK, a fast and scalable high-order solver for computational fluid dynamics. NEK5000, described as “our classic” is mostly Fortran, and nekRS, “our next generation code … an open-source Navier Stokes solver based on the spectral element method targeting classical processors and hardware accelerators like GPUs” is mostly C++.
CFD is a common use of Fortran, judging from GitHub. Looking at the source of NEK5000,
dir /s *.f90 says
Total Files Listed: 9 File(s) 232,775 bytes
and dir /s *.f says
Total Files Listed: 309 File(s) 7,902,772 bytes
so it is possible that most of the code were never modernized. I know that one can use modern Fortran features in fixed source form code, but I don’t think this is common. The .f files don’t use allocatable arrays.