That depends on ones definition of 'best'. One could also write:

sub copy_hash {
    my $hr = shift // return {};
    my $copy;
    @$copy{keys %$hr} = value %$hr;
    $copy;
}
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or just:

sub copy_hash {{%{$_[0]//{}}}}
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Or without a sub:

my %copy = %+;
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