flatMap, map, reduce, and filter not a function only when running npm test with jest

I am trying to pass my tests using jest for my javascript project. The server runs perfectly fine when running npm start and hitting various endpoints. However, when I run npm test which calls: cross-env CI=true NODE_ENV=test jest I get errors when using map, reduce, filter, or flatMap in my code. The error is like this:
TypeError: xxx.flatMap is not a function
or
TypeError: xxx.map is not a function
where xxx is 100% an array of array of strings.

I was running node version 14 but upgraded to 16.17.1 and still have this issue.

This is my jest configuration as well as the dev dependencies inside of package.json:

 "devDependencies": {
    "core-js": "^3.31.0",
    "jest": "^29.5.0",
    "jest-junit": "^12.1.0",
    "sinon": "^11.1.1",
    "supertest": "^6.1.3"
  },
  "jest": {
    "setupFiles": [
      "core-js"
    ],
    "collectCoverage": true,
    "testPathIgnorePatterns": [
      "target"
    ],
    "collectCoverageFrom": [
      "**/*.{js,}",
      "!**/node_modules/**",
      "!**/coverage/**",
      "!**/target/**",
      "!**/src/routes/**",
      "!**/src/validators/**",
      "!**/src/models/**"
    ],
    "coverageReporters": [
      "json",
      "lcov",
      "text",
      "cobertura"
    ],
    "reporters": [
      "default",
      "jest-junit"
    ]
  }

What didn’t work so far:

  • Uninstalling jest globally
  • Adding "setupFiles": ["core-js"] to my jest config
  • Installing core-js and adding require('core-js/stable'); at the top of my test file and the file that using map/flatMap/filter/reduce
  • npx jest --clearCache
  • Creating a jest.config.js file at the root of my project with the config and require('core-js/stable'); at the top and passing --config jest.config.js to my npm test script
  • running npm install jest@latest --save-dev and npm install core-js@latest --save-dev
  • deleting node_modules and running npm install again after all of the above

Not sure what to do next. I can obviously switch to for loops but this is killing me. Why is jest not working but the server works fine normally with map, filter, reduce, and flatMap??? So lame