I just installed R2019b and the help function does not work. Example: I created the addme function from the Add Help for Your Program page in the documentation. Result:
>> help addme
addme is a function.
c = addme(a, b)
The help text in the file was not shown. Also:
>> help help
help not found.
A similar question was asked before, but the answer was not very helpful for me.
help seems to work ok for built-in functions.