The block and layout reference in the panel

Blocks & layouts, in the sidebar, is at /cms/gallery.

The page lists every block available on the site, grouped by category (Data, Interactive, Layout, Media and Text), each with a preview rendered with sample content and a table of the fields it takes. It also lists every layout with the regions it offers. The page is generated from the site's own configuration, so it always matches the blocks and layouts installed.

Use it to see what a block looks like before adding it, or to choose between two similar blocks. Where this guide and that page disagree, that page is correct: it describes this site specifically, and this guide describes the CMS in general.