Deliberate, and narrower than it looks: --pm only chooses which package manager performs the install of the SDODS packages. It has nothing to do with the package manager your own projects use, and it does not go near your repos.
Pick npm and nothing else changes on the machine — it ships with Node, which you already need:
bash
curl -fsSL https://sdods.com/install.sh | sh -s -- --pm npm
The default is bun, which the installer will install into the SDODS home if you do not have it. If you would rather it did not, --pm npm is the flag that prevents that.
To be explicit about the part that worries people: SDODS does not require a lockfile, a workspace field or a package manager in your test repository. A workspace scaffolded by sdods init is project YAML, environment YAML and feature files. Your yarn setup and this flag never meet.