Differnces between cjs, umd in react

I debugged react package.
Write in two places debugger; code.
cjs/react.development.js
umd/react.development.js

//cjs
'use strict';

debugger;

if (process.env.NODE_ENV !== "production") {
  (function() {

          'use strict';

//umd
(function (global, factory) {
  typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
  typeof define === 'function' && define.amd ? define(['exports'], factory) :
  (global = global || self, factory(global.React = {}));
}(this, (function (exports) { 'use strict';
  var ReactVersion = '18.2.0';

  debugger;

But it only debugged cjs file debugger.

Why is not checked umd file debugger ? And what is differenec between cjs and umd ?

extra : Does CRA not allow to debugger in node_module folder's package?
I coulnd't debug for CRA project, i built react project without CRA then debugger finally worked.

1. Differnces between cjs, umd in react
2. Does CRA block debugger in node_module's package ?

Thank you for reading.