Add generatePackageJson to build target's options

project.json

{
  "root": "apps/api",
  "sourceRoot": "apps/api/src",
  "projectType": "application",
  "targets": {
    "build": {
      "executor": "@nrwl/node:build",
      "outputs": [
        "{options.outputPath}"
      ],
      "options": {
        "outputPath": "dist/apps/api",
        "main": "apps/api/src/main.ts",
        "tsConfig": "apps/api/tsconfig.app.json",
        "assets": [
          "apps/api/src/assets"
        ],
        "generatePackageJson": true
      }
      ...
}