Does not seem to work with single package installs

[CxRes]

I tried this with a new project and I get the following result. Please look especially at the npm i below:

PS D:\dev> npm run preinstall                                                                        
> @ preinstall D:\dev
> npx only-allow pnpm

npx: installed 26 in 8.997s
╔═════════════════════════════════════════════════════════════╗
║                                                             ║
║   Use "pnpm install" for installation in this project.      ║
║                                                             ║
║   If you don't have pnpm, install it via "npm i -g pnpm".   ║
║   For more details, go to https://pnpm.js.org/              ║
║                                                             ║
╚═════════════════════════════════════════════════════════════╝
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! @ preinstall: `npx only-allow pnpm`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the @ preinstall script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.

npm ERR! A complete log of this run can be found in:
npm ERR!     C:\******\AppData\Roaming\npm-cache\_logs\2020-06-27T22_06_14_067Z-debug.log


PS D:\dev> npm i dotenv
npm notice created a lockfile as package-lock.json. You should commit this file.

+ [email protected]
added 425 packages from 258 contributors and audited 444 packages in 207.81s

75 packages are looking for funding
  run `npm fund` for details

found 0 vulnerabilities

Versions: node: 14.4.0 npm: 6.14.5 OS: Windows 10 x64

Perhaps you might like to look (or perhaps have already looked) at the thread here: https://stackoverflow.com/questions/41076172/force-yarn-install-instead-of-npm-install-for-node-module/