Someone coming here in 2024 (or after) protobufjs v 7.x.x has removed the cli pbjs. You need to install it separately.
Check out https://www.npmjs.com/package/protobufjs-cli

To use pbjs in the package.json install it using npm i protobufjs-cli and
To use pbjs directly then install global using npm i -g protobufjs-cli