Cannot start observer: (UndefinedFunctionError) function :observer.start/0 is undefined

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3

Done, but :observer.open() results in the following error:

{:error,
 {:undef,
  [
    {:observer_backend, :sys_info, [], []},
    {:observer_sys_wx, :init, 1, [file: ~c"observer_sys_wx.erl", line: 50]},
    {:wx_object, :init_it, 6, [file: ~c"wx_object.erl", line: 404]},
    {:proc_lib, :init_p_do_apply, 3, [file: ~c"proc_lib.erl", line: 240]}
  ]}}

Any idea why?