The trainer is made for the basic game only. The definitive edition is a new game, sold separately. It would require a new game request.
If you take a look at Grim Dawn: Definitive Edition Steam page, you will see that it is not a new game. it a bundle to purchase the main game and the DLCs together at the discount rate. And scroll down to see the list of separated game and DLCs, and it didn't have it own review section as well.
And I have the main game and the DLCs before the "Definitive Edition" came out and it automatically given the "Definitive Edition" to me because I have those things and they are still a bundle. The library page of Grim Dawn doesn't show the definitive edition, only showing me the main game "Grim Dawn". Shadow of the Tomb Raider: Definitive Edition are basically the same thing, a bundle to purchase the main game and the DLCs together at the discount rate.
However, there are legit definitive edition games that are entirely new game such as Age of Empires II and Divinity: Original Sin 2. It just the publisher/developer decided to use "Definitive Edition" as the new game to sell more whereas it is not such as Grim Dawn and Shadow of the Tomb Raider in this case.