@EduardoRFS ack. Actually, Dune does the same for cross-compilation. More precisely, when compiling with -x <target>, or when setting up cross compilation via the dune-workspace file, it reads the corresponding findlib.conf file installed by the OCaml cross-toolchains and cross-packages · GitHub opam repositories.
So it wouldn’t be too difficult to change Dune so that it always read the findlib configuration file. However, there is on-going work to add support for OCAMLPATH in the compiler and eventually deprecate ocamlfind. So moving from using OCAMLPATH to using findlib.conf feels like going backward.