Security enhancements :
- Two-factor authentication (2FA) is now enabled by default for the Magento Admin.
- Template filter strict mode is now enabled by default.
- Data rendering for UI data providers is now disabled by default.
- New \Magento\Framework\Escaper class
- Support for new security.txt file
- PHP 7.4 support introduced and PHP 7.1 and 7.2 deprecated
- Support for PHPUnit 9.x and deprecation of PHPUnit 6.5
- Elasticsearch 7.6.x support
- MySQL 8.0 support
- Removal of the MySQL catalog search engine
- MariaDB 10.4 support
- Migration of dependencies on Zend Framework to the Laminas project
- Removal of the core integration of the Signifyd fraud protection code
- core Braintree module has been removed from the code base
- Removal of core integration of third-party payment methods
- Support for partial-word search for Elasticsearch (new default search engine)
- Deprecation and removal of the Web Set Up Wizard
- Composer update plugin
- Seller-assisted shopping
- Improvements to customer data section invalidation logic
- Multiple optimizations to Redis performance.
- Improved caching of results of SQL queries to inventory tables
- Improvement of up to 25-30% to Quick Order add-to-cart performance.
- Adobe Stock Integration v2.0
- New Media Gallery
- Inventory Management
- PWA Studio
Other, for more information refer Magento official devDocs