There are now 42 Full Site Editing (FSE) themes published on wordpress.org. The most recently added show 0 downloads in December, and a few in January.
The theme with the most downloads, Emulsion, is a hybrid theme which has been around for year. You can either use it as a classic theme, or switch to Full Site Editing.
What’s missing from this chart is Twenty Twenty-Two, due for release on 25th January 2022.
FSE theme listings
themes.gutenberghub.com has an advanced user interface showing the colour palettes, typography, and block shapes and styles.
The official repository for themes approved for delivery from WordPress.org is wordpress.org/themes/tags/full-site-editing/