Here's how I'd determine the max depth of a Perl nested hash/array structure:

use Carp qw/croak/;
use List::Util qw/max/;

sub max_depth
{
    my $thing = shift;
    croak "too many arguments" if @_;
    
    my $children = do {
        if (ref $thing eq 'ARRAY')    { $thing }
        elsif (ref $thing eq 'HASH')  { [values %$thing] }
        else                          { undef }
    };
    
    return 1 + max map { max_depth($_) } @$children
        if $children;

    return 0;
}

my $data = {
    foo => [1, 2, 3],
    bar => [4, 5, { quux => { quuux => 6 } }],
    baz => 7,
    };

print max_depth($data->{bar}[2]{quux}{quxux}) . "\n";
print max_depth($data->{bar}[2]{quux}) . "\n";
print max_depth($data->{bar}[2]) . "\n";
print max_depth($data->{bar}) . "\n";
print max_depth($data) . "\n";

__END__
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