The failure is recognising 'bar' as a scalar rather than a hash and is (i think) nothing to do with 'baz' being a scalar or array.

bar is an unquoted string, baz is an unquoted string.
$foo->{bar} is a scalar, holding a hash reference.
%{ $foo->{bar} } is the hash to which $foo->{bar} is refering.
$foo->{bar}->{baz} is a scalar.

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