Oops, I thought he wanted to group by quantity. To group by presence/absence (presence first), it's simplest to solidify the concept into values that can be compared with <=> or cmp. Let's pick zero for presence and one for absence (since zero comes before one).

my $pro_products = $products{Cat}{Pro};

sort { 
    $pro_products->{$a}{Qua} ?0:1 <=> $pro_products->{$b}{Qua} ?0:1
        ||
    $a cmp $b
}
keys %$pro_products
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Update: Down below, L~R picked "A" and "B" instead of 0 and 1. Same idea.