Can you please point me to some documentation or examples where Intel Fortran is used to offload to, say, NVIDIA GPUs? I don't think it supports it yet.
PGI and IBM support CUDA Fortran, other compilers don't. PGI/Flang has an experimental support for offloading "do concurrent". Some compilers also support the openmp/openacc pragmas and GPU offloading. One can also call CUDA C from any Fortran compiler via iso_c_binding. None of this is ideal.
I think it's still a research problem how to best integrate GPU support in the language itself. CUDA Fortran is nice --- one thing we want to do down the road is to implement CUDA Fortran and to allow LFortran to transform code it understands into a Fortran dialect that all Fortran compilers can compile, so that one can use any Fortran compiler and still use CUDA Fortran.
The other path is to parallelize "do concurrent", but part of this is also means to extend Fortran to allow to specify the array layout, as Kokkos (https://github.com/kokkos/kokkos) allows.
That is one of the biggest problem with Fortran: people want to be assured that their code will run on modern hardware. When using, e.g., C++ and Kokkos, then there is some assurance that the code will run.