Only Pokemon that have a Gigantamax form can have the Gigantamax Factor, so it's impossible to get a Gigantamax Factor Ditto. According to Bulbapedia:
If a Pokémon transforms into a Dynamax Pokémon, it will successfully transform but not become Dynamaxed. Transformed Pokémon can Dynamax, unless they are transformed into Zacian, Zamazenta, or Eternatus; if the user is already Dynamaxed, Transform will fail against these three Pokémon. Transform does not copy the Gigantamax Factor, so even if a Pokémon transforms into a Pokémon that can Gigantamax, the transformed Pokémon will be able to Dynamax but not Gigantamax. If the target is Eternamax Eternatus, the user transforms into the regular version of Eternatus.
Source
The Transformed Ditto could Dynamax, but not Gigantamax.
