Luma and Hyva are two completely different themes for Magento 2. Luma is a base theme distributed with Magento. Its main advantage is that all extensions are developed with full support for Luma by
Magento Hyvä Migration Made Easy: Best Practices for a Smooth Transition
Hyvä is a modern Magento 2 theme developed to improve performance and page load speed. It is built using Tailwind CSS and Alpine.js - cutting-edge technologies that help reduce complexity and code size compared to ordinary Magento 2 themes.
The usage of up-to-date approaches for web development makes Hyvä flexible and easy to maintain. Moreover, it significantly enhances the user experience on the website thanks to streamlined page load times and smooth navigation.