"That" is simply a determiner. You can replace it with any other determiner and you will have an equally good sentence: "There's a new superhero" "There's the new superhero" "There's that new superhero" "There's this new superhero" "There's some new superhero" "There's my (your, his, etc.) new superhero" Using "that" has an effect similar to pointing your finger at the object to identify it.

In the sentence "There's that new superhero movie and the romantic comedy that everyone's been talking about," the phrase "There's that" is a conversational and informal way to introduce or point out something familiar or previously mentioned in context. Breaking it down: "There's" is a contraction of "there is," used to indicate the existence or presence of something. "That" refers to something specific the speaker assumes the listener already knows about or can easily recognize. Function in the sentence: Together, "There's that" suggests that the speaker is calling attention to two specific options: the superhero movie and the romantic comedy. It has a casual, conversational tone that implies these options may already be familiar to the listener or are widely known in the current context. Rephrased Example: "The new superhero movie and the romantic comedy are showing this weekend." Or, "Oh, there's the new superhero movie and the romantic comedy everyone’s been talking about." It’s common in casual speech when discussing options or known topics.