Next I will analyze what is seen in the preview and I will comment on some predictions I have, I think they can be very accurate so [this analysis has possible spoilers].
Something that makes us clear the trailer is that it will be very different from what we had seen so far, it is true that each Joker had a different representation, but this seems the most realistic so far. It shows us a simple man who has a difficult life, who is tired and who had enough of life and how society works.
As far as can be seen, the strongest reasons for this are the health of his mother and his bad economy to take care of her better, the mental illness of the protagonist that he mentions when he is seen writing jokes about a note-taker, and the constant abuse he receives because of that for several people.
Fed up with society, this man loses control and feels forced or decides to do something about it, something that leads him to commit crimes, including murder. Worthy of the Joker.
Some things that are perhaps more subtle in the trailer are the crowds of people you see in a couple of scenes, you see several people with posters, illustrations and clown masks with the same makeup. Clearly manifest to support what the Joker tries to promote. Surely using methods of mass manipulation, psychological or simply taking advantage of the bad situation try to start a revolution.
What I am sure of is that this version of the Joker will have more social and political overtones than the previous ones, together with a psychological instability closer to reality.
A very important scene that we also see is the protagonist with a child separated by bars, this guy is Bruce Wayne, confirmed, I noticed when looking for the cast hahaha. This makes a theory that says that this Joker is not the one we know but the one that inspires the true one. Also the man who sees that the man talking on TV is the father, Thomas Wayne, who is still alive at the moment. Maybe we will even see in this film his death possibly at the hands of this version of the Joker or because of those who support him