Reply To: WordPress – modify title tag.

[Ilan Firsov]

Not really sure but from a little search (https://developer.wordpress.org/reference/hooks/wp_title/)[wp_title filter] should still work, maybe try that.

<?php
add_filter( 'wp_title', 'my_new_title', 10, 3 );
function my_new_title( $title, $sep, $seplocation ) {
    return "123 {$sep} {$title}";
}