You can take a peek at the internal structure by using IO.inspect/2 and it’s option structs:

iex(7)> NaiveDateTime.utc_now() |> IO.inspect(structs: false)
%{
  __struct__: NaiveDateTime,
  calendar: Calendar.ISO,
  day: 17,
  hour: 12,
  microsecond: {614456, 6},
  minute: 37,
  month: 9,
  second: 47,
  year: 2019
}

That’s how all structs work in Elixir.

Structural comparison of dates was actually used as an example of the new type system when it was introduced! At the moment I don’t believe it can catch this within a function like Enum.min_by() (obviously since it didn’t for you), but there are more type system changes coming in 1.19 and 1.20 which have to do with functions, so perhaps it will eventually?

Yes: CompareChain — compare_chain v0.6.0

The OP would be:

import CompareChain

datetime1 = ~N[2019-09-26 01:00:00.000000]
datetime2 = ~N[2020-01-24 00:00:00.000000]
compare?(datetime1 > datetime2, NaiveDateTime) #=> false

From the erlang documentation:

Maps are ordered by size, two maps with the same size are compared by keys in ascending term order and then by values in key order. In maps key order integers types are considered less than floats types.

This means in structural comparison the :day key has precedence over the :month key. So for any value in :month the higher :day value will sort last.