ÄÖÜẞ
<a href="//" title="&Auml;&Ouml;&Uuml;&#x1E9E;">ÄÖÜẞ</a>
<img src="/a.jpg" alt="&Auml;&Ouml;&Uuml;&#x1E9E;">

#! /opt/perls/perls/perl-5.38.2/bin/perl
use strict;
use warnings;
use 5.038;

use utf8;

use CGI::Carp qw( fatalsToBrowser );
use CGI;
use HTML::Restrict;

my $html = do { local $/; <DATA> };
my $cgi = CGI->new();
my $hr = HTML::Restrict->new( rules => {
    a   => [ qw( href title ) ],
    img => [ qw( src alt ) ],
});

my $processed = $hr->process($html);

binmode(STDOUT,':utf8');

say $cgi->header({
                -type => 'text/html',
                -charset => 'UTF-8',
        }),
        $processed;


__DATA__
ÄÖÜẞ
<a href="//" title="ÄÖÜẞ">ÄÖÜẞ</a>
<img src="/a.jpg" alt="ÄÖÜẞ">