OpenMP support in Fortran will improve as flang matures. In OpenMP 5.0 "#pragma omp requires unified_shared_memory" was introduced. At LLNL, they are are currently building El Capitan (https://www.datacenterknowledge.com/supercomputers/lawrence-...), a supercomputer using AMD MI300A accelerators which support this concept. LLNL is also one of the OpenMP ARB members (https://www.openmp.org/about/members/).