When turning on the opam file generation, if the dune dependency is explicitly specified no check is being done on whether or not the dune dependency actually has a correct constraint.
For instance:

$ ls
$ cat dune-project
(lang dune 2.4)
(name test)

(generate_opam_files true)

(package
  (name test)
  (depends dune))
$ dune build
$ cat test.opam
# This file is generated by dune, edit dune-project instead
opam-version: "2.0"
depends: ["dune"]
[...]

Here the opam file is generated with an explicit dependency to dune with no constraint. In my opinion it should be checked that >= 2.4 or above is being required. It would simplify opam-repository maintenance. For example see this PR in which the case was hit: ocaml/opam-repository#16280