Can this patch be applied yet?  It is one of those beautiful fixes that only removes code.

Here is a changeset that implements Mike's change, and gives a comment explaining the problem for nested functions.

(file #37547)

To replicate:

• in file Foo.m:

function Foo
% Function Foo help header
  disp('hello from Foo');
  Bar;
  Fizz;

  function Fizz
  % Nested Function Fizz help header
    disp('hello from Fizz');
  end
end

function Bar
% Subfunction Bar help header
  disp('hello from Bar');
end

• at the terminal:

>> help Foo>Bar
error: help: 'Foo>Bar' is not documented

>> help Foo>Fizz
error: help: 'Foo>Fizz' is not documented
>>

• (matlab output for reference):

>> help Foo>Bar
  Subfunction Bar help header

>> help Foo>Fizz
  Nested Function Fizz help header

The error seems to stem from get_help_text which is a built-in (libinterp/corefcn/help.cc), called by help.m
This seems to return format = "not documented" back to help.m instead of a more appropriate value.