@babel/plugin-proposal-optional-chaining-assign enables Babel to transpile the optional chaining assignment operator (??=) in JavaScript. This operator allows for concise assignment when a value is nullish (null or undefined). It simplifies code by assigning a right-hand-side value only if the left-hand-side variable is nullish, avoiding potential errors and improving readability. Integrating this plugin allows developers to smoothly use this modern JavaScript feature while maintaining compatibility with older environments.