How to use native datetime (datetime-local) input as Wolfram Mathematica / Wolfram Cloud FormFunction field's control (as opposed to a smart input field).

DateTimeFormFunction.md

FormFunction[{
  "date" -> <|
    "Interpreter" -> "String",
    "Control"     -> Function @ EmbeddedHTML @ StringTemplate[
        "<input type='datetime-local' id='id_`1`', name='`1`' value=`2` step='1'>"
     ]["date", DateString["ISODateTime"] ]
  |>
}
, ToString @ DateObject @ #date&
]