Let me put things in this perspective.

It’s not realistic to expect to be able to put trigger warnings for a large population of strangers on the internet. You’re right; when putting it in blanket terms like that, it is silly.

However, there are two things where you could be mindful of others. The first are talking about highly prevalent and violent topics in detail: rape, csa, domestic abuse springs to mind. Things where you probably either know of, or have heard of, someone suffering long term as a direct result of the trauma these events inflict.

But if that’s still too broad for you, then you should keep your close friends and family into consideration and talk to them if you know one of them has gone through an extremely difficult life event. If nobody in your personal circle has experienced such things, then like the other commenter said: I’m very happy for you and them. If someone has, then even just saying “Hey do you want a heads up if this topic comes up in our group chat?” is enough. Maybe they’ll say yes. Maybe they’ll say no. But now you know what their wishes are and can act accordingly with respect to that.

Honestly that’s all people really want, I think.