open my $out_fh, ">:encoding(UTF-8)", $opt->{out} or croak    "Can't open file $opt->{out}!";
...

nstore_fd $data, $out_fh;

...
close $out_fh;

##</code><code>##

"\x{00f0}" does not map to utf8 at /usr/lib/perl5/site_perl/Storable.pm line 303."

##</code><code>##

$Storable::drop_utf8 = 1;