allow email address to be used as login name

email-address-login.php

<?php
add_filter ( 'authenticate', 'rkv_login_options', 20, 3 );

function rkv_login_options( $user, $username, $password ) {

    if ( is_email( $username ) ) {
        $user	= get_user_by( 'email', $username );
    }
  
    if ( $user ) {
        $username = $user->user_login;
    }

    return wp_authenticate_username_password( null, $username, $password );
}

Worth removing the authenticate filter first or else you get an PHP error: "Notice: Undefined property: WP_Error::$user_login....."

remove_filter( 'authenticate', 'wp_authenticate_username_password', 20, 3 );

Also for the Label and error message you can add these filters.

function anagram_username_or_email_login_new( $translated, $original, $domain ) {
   if(in_array( $GLOBALS['pagenow'], array( 'wp-login.php', 'wp-register.php' ) ) ){
        if(  $translated == 'Username' ) {
             $translated = __( 'Username or Email', 'anagram' );
        }
    }
   return $translated;
}
add_filter( 'gettext', 'anagram_username_or_email_login_new', 10, 3 );

add_filter( 'wp_login_errors', 'anagram_incorrect_username_message', 10, 2 );
function anagram_incorrect_username_message( $errors, $redirect_to ) {
    if( isset( $errors->errors['invalid_username'] ) ) {
        $errors->errors['invalid_username'][0] = sprintf( __( '<strong>ERROR</strong>: Invalid Username or Email. <a href="%s" title="Password Lost and Found">Lost your password</a>?' ), wp_lostpassword_url() );
    }
    if( isset( $errors->errors['empty_username'] ) ) {
        $errors->errors['empty_username'][0] = '<strong>ERROR</strong>: The username/Email field is empty.';
    }

    return $errors;
 }