The new editor has a few different views to cater to every editor’s preferred writing environment. By opening the options in the top right, it enables you to choose between the visual editor and the code editor (Ctrl+shift+alt+m). The code view will display the block syntax denoted by HTML comment tags (i.e. <!-- wp:example -->). Be careful when editing the syntax – broken tags will trigger your blocks to be changed into the ‘classic’ block.
Each editor can choose one or more view options; ‘Top Toolbar’ (move all the block options to the sticky top menu), ‘Spotlight Mode’ (grey out the blocks you’re not working on) and ‘Fullscreen Mode’ (hide the rest of the site options).