like it says in the error, the trainer is made for Steam, which you are not running the game from it seems.
if you want a trainer for a different platform you can request it.
To submit a request for a new distribution platform, please use our trainer requests system. Once at least 5 people request the same distribution, it will be available for funding. Please do NOT use the trainer option request system to request new platforms as they will be denied. Premium members at any level may request a new distribution as long as it’s done through the normal request system.