Attributes for Blocks

In your selected block’s inspector controls (Block settings) scroll all the way to the bottom and click on “Advanced”. It should contain a section called “Additional attributes”.
Type an attribute name into the “Add attribute” field and press “Add” to add an attribute for the block. A new input with the attribute’s name should appear below, into which you can optionally insert the attribute value.
Example attributes: style, title, target, class, id, onClick, data-*, aria-*.

For regular blocks, attributes are added to the block save content’s root element, meaning they will be rendered only on the front end and not in the editor. For dynamic blocks the attributes are added via render_callback function and they may also be applied in the editor, depending if the block is rendered server or client side.

It should work with normal blocks that render a valid WP Element that can utilize the blocks.getSaveContent.extraProps filter as well as dynamic blocks that utilize a render_callback. Third party blocks that do something unorthodox may not work.
Known unsupported blocks

@ prefix in an attribute name is used for “override” mode in this plugin, for Alpine.js attributes use x-on:click instead of @click or use the shorthand syntax with two @ characters instead of one: @@click.

The afb_unsupported_blocks filter can be used in your child theme’s functions.php file to disable block support for adding additional attributes.

add_filter('afb_unsupported_blocks', function($blocks) {
    $blocks[] = 'core/button';
    return $blocks;
});

Blocks with custom attributes may become invalid, depending on which attributes you’ve added. From there you can recover the block without the custom attributes by clicking “Attempt Block Recovery” or keep the block with custom attributes as HTML by choosing “Convert to HTML”. If you don’t want to risk blocks becoming invalid you need to remove all custom attributes before disabling the plugin.