"Fwiw the change of quoting you suggested doesn't actually fix my mistake."

My apologies if the change in quoting was misinterpreted as part of the fix.

The change from //vm to //matrix/vm was the fix.

You had multiple instances of \' and \@ (within double-quoted strings) throughout your post: the quoting change was a cure for backslashitis. :-)

Here's the test I ran prior to posting:

#!/usr/bin/env perl -l

use strict;
use warnings;

use XML::LibXML;

my $file = 'pm_1082058_n4000-small.xml';
my $parser = XML::LibXML->new();
my $doc = $parser->parse_file($file);

for my $vm ($doc->findnodes('//matrix/vm[@type="br"]')) {
    my $version = $vm->findvalue('./release/@version');
    print  'Version: ', $version;
    print  'Wanted:  ', $vm->findvalue('./release/@wanted');

    if ($version eq '7.2.1') {
        print 'Found!';
        last;
    }
}
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Output:

Version: 7.2.2
Wanted:  
Version: 7.2.1
Wanted:  YES
Found!
[download]

As you can see, there's no backslashes here at all (which I find makes the code more readable). The '//matrix/vm[@type="br"]' solution which I posted in my original reply was copied directly from that. If you want to run that test (or modifiy it for other tests), the data I used (pm_1082058_n4000-small.xml) is in the spoiler below.

<formation name="stoneridge" version="1.6">
  <block> 
    <matrix>
      <vm type="sns">
        <release version="8.5.e">
          <supported>
            <fixed>123.1106</fixed>
          </supported>
        </release>
      </vm>
      <vm type="br">
        <release version="7.2.2">
        </release>
      </vm>
    </matrix>
    <notmatrix>
      <vm type="sns">
        <release version="4.1.e">
          <supported>
            <min>124.1306</min>
            <max>124.1500</max>
          </supported>
        </release>
      </vm>
      <vm type="br">
        <release version="7.2.1" wanted="NO">
        </release>
      </vm>
    </notmatrix>
    <matrix>
      <vm type="sns">
        <release version="4.1.e">
          <supported>
            <min>124.1306</min>
            <max>124.1500</max>
          </supported>
        </release>
      </vm>
      <vm type="br">
        <release version="7.2.1" wanted="YES">
        </release>
      </vm>
    </matrix>
  </block>
</formation>
[download]

Ah, thanks, understood. Yes, the de-backslashed code is much easier to grasp. And thank you for pointing the xpath element fix.