The category description is displayed on every page of the category archive by default.

If you』d like to display them on the first page of the archive only, try this PHP snippet below:

add_action( 'wp', function() {
$page = (get_query_var('paged')) ? get_query_var('paged') : 1;
if ( 1 !== $page ) {
remove_action( 'generate_archive_title', 'generate_archive_title' );
add_action( 'generate_archive_title', 'tu_custom_paged_archive_title' );
};
}, 20 );

function tu_custom_paged_archive_title() {
?>

<?php
}