In June 2021 there were only 7 FSE themes on wordpress.org/themes. Many others were being developed.
WordPress.org
- Armando
- Blockbase
- Block-Based Bosco
- Hansen
- Naledi
- Q
- TT1 blocks
Theme-experiments
- Emptytheme
- FSE tutorial
- Phoenix
- Photo Blocks
- Twenty Nineteen Blocks
- Twenty Twenty Blocks
Automattic themes
- Ibis ( maybe?)
- Mayland Blocks ( child theme)
- Quadrat ( child theme )
- Seedlet (Blocks)
Other
- Fizzie
- SB
- ThisIs…