Here you go:

defmodule Example do
  def sample(acc \\ %{}, data, info)

  # in case nested value does not exists
  def sample(acc, nil, _info), do: acc

  # instead of above you may want to use another code
  # as it would place a nil value for each nested info who does not exists in data you passed
  # 
  # def sample(acc, nil, info) when is_atom(info), do: Map.put(acc, info, nil)
  # def sample(acc, nil, info) when is_list(info), do: Enum.reduce(info, acc, &sample(&2, nil, &1))
  # 
  # def sample(acc, nil, info) when is_map(info) do
  #   Enum.reduce(info, acc, &sample(&2, nil, elem(&1, 1)))
  # end

  # when we need to fetch a flat list of fields
  # or said list + some extra nested fields
  def sample(acc, data, info) when is_list(info) do
    # there should be no more than one map in info list
    # the map info stores information for nested fields
    # the remaining items is a list of fields to take from current data
    groups = Enum.group_by(info, &is_map/1)
    [map_info] = groups[true] || [%{}]
    groups[false] |> Enum.reduce(acc, &Map.put(&2, &1, data[&1])) |> sample(data, map_info)
  end

  # here we are reducing info map over our acc
  # which means all nested fields logic goes here
  def sample(acc, data, info) when is_map(info) do
    Enum.reduce(info, acc, fn {info_key, info_value}, acc ->
      sample(acc, data, info_key, info_value)
    end)
  end

  # this clause would match if we want to fetch just one nested field
  defp sample(acc, data, info_key, info_value) when is_atom(info_value) do
    Map.put(acc, info_value, get_in(data, [info_key, info_value]))
  end

  # in any other case we have a map or list which we already support
  # so all we need to do is to call the same logic, but with nested data
  defp sample(acc, data, info_key, info_value) when is_list(info_value) or is_map(info_value) do
    sample(acc, data[info_key], info_value)
  end
end

data = %{
  gps: %{
    lat: 48.857144,
    lon: 2.340242,
    altitude: 35.0
  },
  metadata: %{
    payload: %{
      content: "1aff4c0002154a080bff4c0010774058308876aa3a29",
      scantime: 1_644_362_438
    },
    macaddress: "B8:C0:78:CD:12:AB",
    receivetime: 1_663_000_169,
    tags: "v1.2,test.app"
  }
}

info = %{gps: [:lat, :lon], metadata: [%{payload: :scantime}, :receivetime], a: %{b: :c}}
iex> Example.sample(data, info)

This code would automatically pick data you need by simply passing an info. Also if you want to add something to result you simply can pass it as first argument which means that you can call this function multiple times for different data:

data1
# without passing acc
|> Example.sample(info1)
# with acc (result of above pipe)
|> Example.sample(data2, info2)

Helpful resources:

1. is_atom/1, is_list/1 and is_map/1 guards
2. Enum.reduce/3
3. Map.put/3