How to display *block number* instead *date value* on WordPress posts?

I have no idea what a ‘block number’ is, but when themes output the date for a post they will use either the_date() or the_time() (or both). You can replace the output using the filters the_date() or the_time():

add_filter(
    'the_date',
    function( $the_date, $format ) {
        $block_number="whatever a block number is";
        
        return $block_number;
    },
    10,
    2
);