validation.sample.1.ts

type Input = {
  trainTripId: string
  pax?: Pax
  startDate?: Date
  travelClass?: string
}

const validateStateProposition = ({
  pax,
  startDate,
  trainTripId,
  travelClass,
}: Input) =>
  pipe(
    sequenceT(E.getValidation(NA.getSemigroup<FieldValidationError>()))(
      pipe(
        validateId(trainTripId),
        E.mapLeft(toFieldError("trainTripId")),
        E.mapLeft(NA.of),
      ),
      pipe(
        E.valueOrUndefined(travelClass, TravelClassDefinition.create),
        E.mapLeft(toFieldError("travelClass")),
        E.mapLeft(NA.of),
      ),
      pipe(
        E.valueOrUndefined(startDate, FutureDate.create),
        E.mapLeft(toFieldError("startDate")),
        E.mapLeft(NA.of),
      ),
      pipe(
        E.valueOrUndefined(pax, PaxDefinition.create),
        E.mapLeft(toFieldError("pax")),
        E.mapLeft(NA.of),
      ),
    ),
    E.mapLeft(combineValidationErrors),
    E.map(([trainTripId, travelClass, startDate, pax]) => ({
      trainTripId,
      pax,
      startDate,
      travelClass,
    })),
  )

validation.sample.2.ts

type Input = {
  trainTripId: string
  pax?: Pax
  startDate?: Date
  travelClass?: string
}

const validateStateProposition = ({
  pax,
  startDate,
  trainTripId,
  travelClass,
}: Input) =>
  pipe(
    Do(E.getValidation(getMonoid<FieldValidationError>()))
      .sequenceS({
        trainTripId: pipe(
          validateId(trainTripId),
          E.mapLeft(toFieldError("trainTripId")),
          E.mapLeft(NA.of),
        ),
        travelClass: pipe(
          E.valueOrUndefined(travelClass, TravelClassDefinition.create),
          E.mapLeft(toFieldError("travelClass")),
          E.mapLeft(NA.of),
        ),
        startDate: pipe(
          E.valueOrUndefined(startDate, FutureDate.create),
          E.mapLeft(toFieldError("startDate")),
          E.mapLeft(NA.of),
        ),
        pax: pipe(
          E.valueOrUndefined(pax, PaxDefinition.create),
          E.mapLeft(toFieldError("pax")),
          E.mapLeft(NA.of),
        ),
      })
      .done(),
    E.mapLeft(combineValidationErrors),
  )

I would say that sample 2, Do notation seems more verbose up front as we build the initial object and require return,
however it is a bit easier to reason about, instead of having to deal with tuples like in the first sample.
In the first sample we also still have to convert the tuple back to an Object.