Here is my version (not sure what all that split stuff was all about):

use strict;
use warnings;

sub sortit {

    my ($alpha_a, $num1_a, $num2_a) = $a =~ /([a-z]+)(\d+)_(\d+)/;
    my ($alpha_b, $num1_b, $num2_b) = $b =~ /([a-z]+)(\d+)_(\d+)/;
    
    my $retn = $alpha_a cmp $alpha_b;
    return $retn if $retn != 0;
    
    $retn = $num1_a <=> $num1_b;
    return $retn if $retn != 0;
    
    return $num2_a <=> $num2_b;
}

my @list = qw (a1_2 a1_1 a10_10 a2_10 a2_1 a2_2 a10_1 a10_2 a1_10);

my @new_list = sort sortit @list;

print "@new_list\n";
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