$ opam show core | grep ^version
version      v0.16.2
$ cat dune-project
(lang dune 3.11)

(name foo)
$ cat dune
(executable
 (name foo)
 (libraries core))
$ cat foo.ml
open Core

let _f = String.Map.find

let _xxx = String.make

let () = print_endline "Hello, World!"
$ dune build foo.exe
File "foo.ml", line 3, characters 9-24:
3 | let _f = String.Map.find
             ^^^^^^^^^^^^^^^
Error: Unbound value String.Map.find