There is a Gatsby Theme Twenty Twenty One by Reflexjs developer arshad. The WordPress Twenty Twenty One theme is fully block-based theme. Because there are not many examples of Gatsby themes with Gutenberg block editor use, except Gatsby Stater WordPress Twenty Twenty by Henrik Wirth which is a great learning example.
Twenty Twenty-One is a blank canvas for your ideas and it makes the block editor your best brush. With new block patterns, which allow you to create a beautiful layout in a matter of seconds, this theme’s soft colors and eye-catching — yet timeless — design will let your work shine. Take it for a spin! See how Twenty Twenty-One elevates your portfolio, business website, or personal blog. WordPress Themes Directory
The Gatsby Theme Twenty Twenty One github repository documentation describes the theme “with support for Gutenberg blocks, menu and menu locations, customizable blog page and more…” but currently still work in progress!