Don't use XML::Simple. Its documentation itself tells you you shouldn't.

You can use XML::LibXML instead.

#!/usr/bin/perl
use warnings;
use strict;

use XML::LibXML;

my $xml = 'XML::LibXML'->load_xml(location => shift);
for my $username ($xml->findnodes('//username')) {
    print $username->textContent, "\n";
}
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I usually use XML::XSH2, which is a wrapper around XML::LibXML. It simplifies the above code to

open file.xml ;
for //username echo (.) ;
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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