Fix node modules package for Xcode 12 by changing "dependency" from "React" to "React-Core" inside their podspec files.

FixNodeModulesForXCode12.js

/*
* You can add this to your package.json file to run
* after "yarn" or "npm install" like this:
* "scripts": {
*   "postinstall": "node ./FixNodeModulesForXCode12.js",
* }
*/

const fs = require('fs');
const glob = require('glob');

console.log('\x1b[36m%s\x1b[0m', '\n\n\n\n\n\nPOST INSTALL IS RUNNING:');

const NODE_MODULES_DIR = 'node_modules';

// Fix node modules package for Xcode 12 by changing "dependency" from "React" to "React-Core" inside their podspec files
glob(NODE_MODULES_DIR + '/**/*.podspec', {}, function(err, files) {
  if (err) {
    return console.error('Error in post install');
  }

  console.info('Total detected podspec files: ', files.length);
  files.forEach(file => {
    fs.readFile(file, 'utf8', function(fileError, data) {
      if (fileError) {
        return console.error('File error: ', fileError);
      }

      const regex = /\.dependency\s*[",']React[",']/g;

      if (regex.test(data)) {
        console.log(
          '\x1b[33m%s\x1b[0m',
          `Detected podspec with wrong dependency ----> ${file}`,
        );
        const result = data.replace(regex, '.dependency "React-Core"');

        fs.writeFile(file, result, 'utf8', function(writeErr) {
          if (writeErr) {
            return console.error('File write error: ', writeErr);
          }
          console.log(
            '\x1b[32m%s\x1b[0m',
            `Fixed podspec with wrong dependency ----> ${file}`,
          );
        });
      }
    });
  });
});

Kudos
10 months later it is still proving useful 😄