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use warnings;
use strict;
use Test::More;

my @AoH = (
    {'targetL' => 'foisonnement', 'origin' => 'AMG', 'count' => '1'},
    {'targetL' => 'foisonnement', 'origin' => 'IDBR', 'count' => '1'},
    {'targetL' => 'gonfler', 'origin' => 'IWWF', 'count' => '1'},
    {'targetL' => 'due', 'origin' => 'IWWF', 'count' => '1' },
    {'targetL' => 'due', 'origin' => 'IWWF', 'count' => '1' },
);

my @AoHfinal;
my %targets;
for my $h (@AoH) {
    push @AoHfinal, ($targets{$$h{targetL}}={targetL=>$$h{targetL}})
        unless $targets{$$h{targetL}};
    $targets{$$h{targetL}}{origin}{$$h{origin}}++;
    $targets{$$h{targetL}}{count}++;
}
$$_{origin} = join ' ', sort keys %{$$_{origin}} for values %targets;

is_deeply \@AoHfinal, [
    {'targetL' => 'foisonnement','origin' => 'AMG IDBR','count'=>'2'},
    {'targetL' => 'gonfler','origin' => 'IWWF','count' => '1'},
    {'targetL' => 'due','origin' => 'IWWF','count' => '2'},
] or diag explain \@AoHfinal;

done_testing;
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Note you didn't specify the order of the resulting values, both @AoHfinal (so I kept the original order from @AoH), or of the origin values (so I sorted them because it was easier).