So, let's look at Raiders for some act breaks, using some formulaic sentences like "Indy wants":
Act I: Indiana wants to find Abner--but instead discovers that Marion Ravenwood has the Staff of Ra headpiece AND a chip on her shoulder. Irreversible change: he's got a partner now.
Act II: Indy wants to find the Ark--and this desire is to strong that he continues with his quest even after (a) he thinks Marion has died and (b) he discovers she didn't die but doesn't rescue her. Irreversible change: he knows where the Ark is and he picks it over Marion. (Note: Only half of that is irreversible.)
Act III: Having found the Ark, Indy wants it. Here's where Indy digs up the Ark (success) and then gets buried in the Ark room with Marion and lots of snakes (failure). We then get a whole series of success-failures as Indy tries to retake the Ark. Is it on a plane? Or a truck? Finally, Belloq succeeds in getting both the Ark and Marion. Irreversible change: Indy is left totally free and totally alone.
Act IV: Indy wants to rescue Marion--but he can't bring himself to destroy the Ark to do so. Here's a strange thing about this screenplay: in any other Hollywood movie, the hero would choose the girl / to be a good guy, but here, Indy seems to give in to his most Belloq-like nature. Luckily, there's the power of god around to smite the Nazis when Indy fails. But there is still an important change here: instead of approaching the Ark only as a historical artifact, Indy seems to accept its supernatural woohoo. Which is why the final scene is Indy arguing with the government about their treatment of religious objects.So, using the same formulaic sentences (because formula helps when breaking structure, even if you wouldn't want to start every sentence in a short story with "Main character wants") and plugging in some place-holder names (which I've stolen and repurposed from Kingdom of the Crystal Skull), let's break out some acts here.
Act I: Indiana Jones wants to be relevant and exciting when all the world seems to be telling him to hang up his hat and go home. Not just because he's old, but because he's burned as many bridges as he's built. So when Iris Spalko comes to ask for his experience in dealing with Oxley, he jumps at the chance. But what concrete object does Indy want? He wants to find Oxley's secret dig--the one that drove him mad (not that Indy believes that).
Act II: Indy wants the skull that he thinks is an Oxley fake to prove that this whole alien thing is fantasy. After investigating Oxley's booby-trapped house in Mexico, Indy figures out that Spalko is actually a Russian agent, with her own organization muscle behind her, whereas he's just a single guy. What's worse, Indy's old protege shows up leading a rival expedition that turns out to be a complementary one--another Russian group, both as co-worker and rival to Iris's group. (The protege was lured into it by promise of his old mentor being in trouble.) Indy at first thinks that Oxley wants the crazy tech to prove his theories correct. And in the bowels of some department store (whee! department store fight!), Indy finds some evidence left over that Oxley failed to get, evidence which points towards South America.
Act III: If the first act was "Indy wants in," Act III is "Indy wants out." Oxley hasn't gone to South America to find aliens, and when Indy and estranged protege head in that direction, they're kidnapped by Oxley's agents who take them to L.A. (So instead of the red line of global travel transitioning between scenes, part of this scene takes place during that travel.) (And the "clue" that's supposed to lead them to the next place is actually the key to the tech. I see a false reveal here, where Indy gets uncrated at what looks like some South American jungle, but turns out to be an LA garden or film set.) Having accidentally delivered one last part to the Oxley cult (with Jack Parson at the Jet Propulsion Laboratory?), Indy begins to realize the enormity of this power: Oxley won't use aliens to get himself back into the academic game, but to become superhuman. (Like the old Woody Allen joke: I don't want to achieve immortality through my works, I want to achieve it through not dying.) Indy wants to keep Oxley from putting together his alien artifact. Does that mean teaming up with the Russian when they show up? Unfortunately, Iris Spalko is part of Oxley's cult for her own gain, so Indy will have to rely on the person he least wants to rely on--his hotshot, hotheaded protege.
Act IV: Perhaps this act takes place either in the desert, with all the stories of tricksters and UFOs, or in the South Pacific, with its cargo cults and atomic testing grounds. Either way, Indy and protege race against Spalko and Oxley, to try to stop them from tuning the radio to the gods/aliens. Finally believing the truth of this and seeing the potential for World War III, Indy and the protege try to sabotage the item/ritual, which at least allows the item to connect to and reject the cult. Indy wants to live again, but also to see his protege go on after him.