If all you need to do is ensure everyone's on the same versions of the libraries - if you aren't concerned with your supply chain, and you can accept that members of your team are on different platforms and thus getting different wheels for the same version, and you don't have platform-specific dependency requirements - then pinned transitive dependencies are all the metadata you need. pyproject.toml isn't generally intended for this, unless what you're developing is purely an application that shouldn't ever be depended on by anyone else or sharing an environment with anything but its own dependencies. But it would work. The requirements.txt approach also works.

If you do have platform-specific dependency requirements, then you can't actually use the same versions of libraries, by definition. But you can e.g. specify those requirements abstractly, see what the installer produces on your platform, and produce a concrete requirement-set for others on platforms sufficiently similar to yours.

(I don't know offhand if any build backends out there will translate abstract dependencies from an sdist into concrete ones in a platform-specific wheel. Might be a nice feature for application devs.)

Of course there are people and organizations that have use cases for "real" lockfiles that list provenance and file hashes, and record metadata about the dependency graph, or whatever. But that's about more than just keeping a team in sync.