opam install topkg 1.0.7 fails with ocaml 5.0.0

[fblanqui]

opam upgrade
The following actions will be performed:
  ∗ install topkg 1.0.7
Do you want to continue? [Y/n] Y

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
⬇ retrieved topkg.1.0.7  (cached)
[ERROR] The compilation of topkg.1.0.7 failed at "ocaml pkg/pkg.ml build
        --pkg-name topkg --dev-pkg false".

#=== ERROR while compiling topkg.1.0.7 ========================================#
# context     2.1.2 | linux/x86_64 | ocaml-base-compiler.5.0.0 | https://opam.ocaml.org#25bba47d
# path        ~/.opam/5.0.0/.opam-switch/build/topkg.1.0.7
# command     ~/.opam/opam-init/hooks/sandbox.sh build ocaml pkg/pkg.ml build --pkg-name topkg --dev-pkg false
# exit-code   1
# env-file    ~/.opam/log/topkg-438895-e8709d.env
# output-file ~/.opam/log/topkg-438895-e8709d.out
### output ###
# [...]
# pkg.ml: [WARNING] OCaml host-os conf: key ext_obj: undefined, using ".o"
# pkg.ml: [WARNING] OCaml host-os conf: key ext_lib: undefined, using ".a"
# pkg.ml: [WARNING] OCaml host-os conf: key ext_dll: undefined, using ".so"
# pkg.ml: [WARNING] OCaml host-os conf: key ext_exe: undefined and
#                   no C toolchain detected, using ""
# ocamlfind ocamldep -modules src/topkg.mli > src/topkg.mli.depends
# + ocamlfind ocamlc -where > /home/blanqui/.opam/5.0.0/.opam-switch/build/topkg.1.0.7/_build/ocamlc.where
# ocamlfind: Package `threads' not found
# Command exited with code 2.
# pkg.ml: [ERROR] cmd ['ocamlbuild' '-use-ocamlfind' '-classic-display' '-j' '4' '-tag' 'debug'
#      '-build-dir' '_build' 'CHANGES.md' 'LICENSE.md' 'README.md' 'pkg/META'
#      'topkg.opam' 'src/topkg.cma' 'src/topkg.cmi' 'src/topkg.mli']: exited with 10

<><> Error report <><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>
┌─ The following actions failed
│ λ build topkg 1.0.7
└─ 
╶─ No changes have been performed
# Run eval $(opam env) to update the current shell environment

[dbuenzli]

# ocamlfind: Package `threads' not found

This is suspicious. I suspect there's another problem with your setup.

[dbuenzli]

I think you are seeing this issue try an opam reinstall ocamlfind.

I'm closing this feel free to continue the discussion if you think there's another problem.

[fblanqui]

opam reinstall ocamlfind worked indeed. Thank you!