Personally, I think you should make the trigger warning available but not intrusive so it does not spoil gameplay for those who don't need the trigger warnings. Like, if your game includes themes of abuse, it's nice to include that in the game notes for anyone who's mental health could be affected by that. But, if you were to include that info at the start of the game along with the credits, it could be considered a spoiler.
Ultimately, people are responsible for their own mental health. But, if you want to be kind, you can make information like trigger warnings readily available