Hide post date for specific categories in Twenty Seventeen (asked by Marie-Christine Rcd on WordPress Academy Facebook group – June 9, 2022)

functions.php

<?php
function jba_hide_posted_on() {
	if ( in_category( array( 'ma-categorie', 'une-autre-categorie' ) ) ) :
		?>
		<style>.posted-on { display: none; }</style>
		<?php
	endif;
}
add_action( 'wp_head', 'jba_hide_posted_on' );