The following code explicitly stores the list of hash refs into the array referenced by $output{items}.

use strict;
use warnings;
use Data::Dumper;

my $Data =  # simulated output of fetchall_arrayref()
[
    [ 'Valls',     ('more fields')],
    [ 'AUT15605',  ('more fields')],
    [ '10UT15605', ('more fields')],
];
my %output;
@{$output{items}} = map { {title => $_->[0]} } @$Data;
print Dumper(\%output);
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