The best way to explain the end of It: Chapter 2 is to compare it with the novel (better than with the miniseries, because it is another adaptation of the original source), is to see what the main changes have been. And not to see if the movie makes it better or worse, what we are not going to get into (nor are we going to get into who is the most terrifying Pennywise, if Tim Curry or Bill Skarsgard), that this is not a criticism of the film, but to see what it leaves out, why it leaves it out and if that influences the meaning of the film.
In the end, this creature that feeds on our greatest fears becomes a puppy if they are bullied. So they insult him, the clown-headed spider is dwarfing little by little until Mike rips his heart out and crushes that healthy muscle that needs action, the monster turns to dust and the scars of the Losers disappear.
Then they all receive a letter from Stanley in which he explains that he removed himself in the middle so that they could win (and incidentally so that Bev's vision was not complete). And the end of history. All this does not require much explanation. And, yes, the bug is dead and well dead (Andy Muschietti, the director of the film, has said that expanding this universe could only be done with a prequel or prequels). Hence the film does not have post-credit scenes (see, it could have dropped that it was all a dream of Bill's character -James McAvoy-).
So the question we have to ask ourselves is: What is Pennywise's relationship with the Losers in the movie? The question that can also be asked like this: Why do you persecute them? In the movie, he wants to attract Derry at all costs. It's been 27 years and you need to bring them back. He escaped and now he wants revenge.
Do not try to keep them out, as in the novel, because deep down they are afraid of it and they want to come back to end him/her/it. Now it is not the group of boys who could with him, but the group of boys who escaped. Because this time they will not escape. In It: Chapter 2 instead of trying to keep the Losers out of Derry, Pennywise has been a victim of the eagerness to bring them back. They are no longer the boys who kicked his ass, they are the ones who escaped, and he has done everything possible to bring them back.
Then there is Stanley's suicide. In the novel, Stan commits suicide because he is too scared and traumatized to face the idea of returning to Derry and even drops that he is under some kind of residual Pennywise energy: he writes "IT" on the wall with his blood after cutting his own wrists in the movie, however, we find something similar to a martyr, watch now the movie and find out why.
The essence of the original font is all over this movie (it happens like Pet Cemetery). The monster presents itself as what you fear most; and feasts on it. The idea is that the real terror is in our past (when our past has been bad, of course).