We'll create fresh WordPress site with Block Catalog installed. You have 20 minutes to test the plugin after that site we'll be deleted.
On activation, the plugin will prompt you to index your content. You need to do this first before you will be able to see the various blocks used on your site. You can also go to WP-Admin > Tools > Block Catalog to do this yourself. Alternately, you can run the WP CLI command wp block-catalog index
to index your content from the command line.
Once indexed, you will be able to see the different blocks used on your site in the Block Catalog Taxonomy.
Navigating to any Block Editor post type will also show you the list of blocks present in a post.
You can also filter the listing to only show Posts that have a specific block.