@Frederic_Loyer Yes, with-dkml dune build ..., with-dkml opam install ..., etc. will adjust your PATH and other environment variables so Visual Studio Build Tools can be used. Using the x64 Native Tools Command Prompt for VS 2019 should also work. Both are described at Old DkML Documentation Site .
Also, in VSCode, my OCaml extension can’t find my opam switches.