One more variation ;-)

CPAN provides us with Set::CrossProduct, which allows us to write your mk_tuples like this:

use Set::CrossProduct;

sub mk_tuples(\@$) {
    my ($arrayref, $n) = @_;
    [ Set::CrossProduct->new( [($arrayref) x $n] )->combinations ];
};

my @set = qw(A B C); 
my $output = mk_tuples(@set, 2);
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