Description

The is_main_query() conditional function should return false if running inside an external query loop block.

Step-by-step reproduction instructions

Add the following code to your function, then add a query block to your theme outside the post content.

function main_query_show_warning( $block_content, $block ) {
    if ( is_main_query() ) {
        $warning = sprintf(
            '<div style="font-size: 14px; background: red; color: #fff; padding: 2px 6px; font-weight: 700; display: inline-block;">%s</div>',
            __( 'this is a main query' ),
        );

        $block_content = $warning . $block_content; 
    }

    return $block_content;
}

add_filter( 'render_block_core/query', 'main_query_show_warning', 10, 2 );

Screenshots, screen recording, code snippet

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Environment info

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Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes