Recently, Full Site Editing (FSE) has been constantly mentioned daily in many WordPress forums and communities. This feature is considered an outstanding transformation of the way we work with WordPress, including the transition from traditional themes to block themes.
Block Themes, also known as Block-Based Themes, are the themes that are designed to be compatible perfectly with Gutenberg blocks and full-site editing. There are a few block themes since Full Site Editing (FSE) is still currently under development. The present block themes are generally in a basic state, mainly serving the requirement to research and develop FSE's features.
Along with that, a completely new block theme, named Quadrat, has been developed recently by the Automattic team. This is a pretty complete block theme for blogs and podcast websites with an eye-catching look. Among the existing Gutenberg block themes, this theme is seen as one of the few having its own "personality".