There's modern stuff being written in astro(nomy/physics) (I can attest to some of the codebases listed in https://github.com/Beliavsky/Fortran-code-on-GitHub#a

There's modern stuff being written in astro(nomy/physics) (I can attest to some of the codebases listed in https://github.com/Beliavsky/Fortran-code-on-GitHub#astrophysics https://github.com/Beliavsky/Fortran-code-on-GitHub#astrophy... being modern, at least in terms of development), but I'd say C++ likely does have the upper hand for newer codebases (unless things have changed dramatically last time I looked, algorithms that don't nicely align with nd-arrays are still painful in Fortran). I've also heard rumours of Julia and even Rust being used (the latter because of the ability to reuse libraries in the browser e.g. for visualisation), but the writers of these codebases (and the Fortran/C/C++/Java) are unusual—Python and R (and for some holdouts, IDL) are what are most people write in (even if those languages call something else).