I’m kind of in a dilemma. If I was to write a prologue to a fantasy story about the history of the kingdom and the political scope of what is happening there, is it necessarily a bad infodump? All of this knowledge is incredibly important to understand the context of the story, even at the beginning, and I make the narrator explain it in an interesting way (as though he was telling a story around a campfire or something). It’s meant to have a sort of “movie-montage” feel to it. It’s a backstory/history, but it’s meant to have an interesting, almost action-packed feel even though it’s only brief snippets of scenes. (If any of you have watched The Hobbit movies, you understand the beginning prologues are kind of interesting. It’s a bit like that). So, is this a bad infodump, or can it be good if I make it interesting?
It is probably still a bad infodump, at least if you intend to sell the story to a traditional publisher.
Because it is not immediate, we don't know who the main character is, and all the "action" is in the past and has nothing to do with the present.
I have been told (by a real publisher) they he wants his MC up front, page 1, and they want them interacting with other people by page 2. At least a conversation. He doesn't want a "contemplative" opening, or an "in transit" opening (somebody thinking about life, the universe and everything while on the bus to work).
My advice is to dump the reader into the middle of your MC's everyday life, give the MC some normal-life problem to solve that requires human interaction, to help reveal their character. Let the reader figure out what is going on. If the background is truly important, it should affect the actions and decisions of the MC, and the MC can "remember" those pieces as they go. It is okay to leave the reader in the dark and reveal the back story slowly. Not just okay, but better, it builds mystery, and interest.
The problem with infodumps, no matter how interesting you try to make them, is they are just a lot of information you want the reader to memorize, and readers cannot memorize much. You are saying "Remember this guy [you never heard of] wants this girl [you never heard of] but she loves this other guy [you never heard of] because ...
The reader is out. Readers remember things by following the hero they are interested in through scenes and vicariously experiencing, through their imagination, what the hero is experiencing. They remember the scenes, and the people they interacted with, and what was said. They remember what is important, so they only remember the bits of the background story that actually has an impact on the MC and what they do and say.
One thing you can do to aid that is to make some character fairly uninformed about the backstory, so your MC or other characters must explain it, or alternatively, make your MC uninformed about aspects of the backstory, so he needs to be informed about it by other characters. Or some mix like that; nobody knows everything, but due to the mission elements are discovered.
Do not make the mistake of thinking that because some best-selling or famous author got away with something, you can too. JK Rowling is the richest author in the world, but on the craft of writing she is pedestrian, at least for adults. She appeals to the middle grade, non-adult teens especially. On the imaginative front she is stellar, off the charts, very good at combining fantasy and mystery, and that is what has carried her books to #1. After she was rejected by nearly every publisher in England, by her account. (Probably because her writing is pedestrian, and modern publishers don't read very far before pitching stories into their reject pile: Which her book was rescued from, by a publisher's child.)
JRR Tolkien is an excellent writer, also with stellar imagination. I wouldn't count on being a one-in-a-hundred-million writer. If you are, that's great, but you will still have a better chance if you avoid the obvious modern prohibitions that every publisher knows: Don't start with an infodump. Don't try to "make it work". Don't start with a prologue, or wall of text, or wall of dialogue, or a "contemplative" opening.
Open on the MC's normal world, solving their normal world issues, interacting with their culture and other people. Figure out what is actually necessary from the backstory to justify the MC's actions and those of others, and incorporate that as you go. Thousands of best-sellers do it, thousands of good movies do it, you can do it too.
There's a much better way to handle backstory you want your reader to learn. Handled appropriately, you can make learning your backstory not merely tolerable - you can make it something your readers are hungry to find out! The key is, as other answers have mentioned, to drip feed the backstory and context throughout your story.
At the beginning of your story, you don't want your readers to know what's going on. You want to give them just enough that they know you know what's going on. This makes the backstory a compelling mystery, and every little drip you give your readers from then on sheds light on why the main character's story matters.
It's a bit self-indulgent, but anime shows pull this off all the time. In Spirited Away, the main character Chihiro suddenly finds herself trapped working in a magical bathhouse. For the entire first half of the movie, she understand absolutely nothing about how the bathhouse or the magical world it exists in works, and neither does the audience. She eventually learns just enough to break a curse on her family and escape, but even that information is never infodumped. She, and the audience, learn all of it by reading in-between the lines of what happens and inferring how things work. As another example, the show Full Metal Alchemist has an incredibly rich magic system and elaborate world, but the only thing we know after the first episode is how wrong alchemy can go when used carelessly. The story ultimately includes elements from grudges from old wars that have never been forgiven, shadowy cabals that have been using dark magic for generations, desperate wizards willing to throw away their humanity for a taste of more power, and the horrifying implications of what powers alchemy - but we know none of this at the start of the show, and all of it is revealed very gradually.
This approach is also used by master writers. Terry Pratchett uses this all the time in the Discworld novels. The Discworld is a fully developed world that's reused across the entire franchsie, and Pratchett doesn't shy away from explaining how the overall world works at the beginning of his novels. But most of the individual novels are focused on one specific mystery. He consistently introduces the question of the mystery at the beginning of the novel, then very gradually chips away at it until one specific and compelling aspect of the Discworld has been explored in detail. In Going Postal, an all-powerful despot finds himself forced to strong-arm a petty criminal into running a post office that's been abandoned for decades. The question at the beginning is, why in the world does the despot need to pull so many strings just to get the mail to go out? By the end of the novel, we learn about a power struggle between the most powerful men in the city, with the post office at the heart of it - but there are only the vaugest hints of this by the time the protagonist shows up at the post office. And in Soul Music, Death becomes caught up in the surreal case of a musician who is simultaneously dead and very much alive, playing the best music anyone has heard in generations. It turns out that the poor bard is being possessed by an ancient entity so powerful that even Death is pushed to his limits struggling against it - but we don't learn exactly what this entity is until the climax! The entire book gradually gives us more and more information about this mystery, so that the reveal feels like meeting an old friend. But the full context isn't given to the reader until the very end.
In Life, the Universe and Everything, Douglass Adams writes about the galaxy being threatened by a violent race of aliens who aim to revive an ancient war using a superweapon that will wipe out all life. We don't find out about the evil aliens, let alone their history or aims, for about half the book. The Lion, the Witch, and the Wardrobe takes us into Narnia and carries the children through the beginning of their adventure before we meet Aslan or learn the full extent of the White Witch's despotic rule. Harry Potter and the Sorcerer's Stone doesn't begin any worldbuilding infodumping at all until Harry escapes the Durselys, and the mystery of the titular Sorcerer's Stone isn't fully solved until Quirrel and Voldermort explain the final missing pieces to Harry in the climax.
In all of these cases, by withholding context and backstory at the beginning and gradually explaining it, the writers keep the audience and readers curious about what's going on. Every time a new piece of information is given out, the readers need to reconsider everything they've learned in its light, and readers are invited to guess at what's truly happening.
Yes, it's bad. Don't do it. Infodumps in the prologue are the sign of a true amateur. To the average reader 'prologue' means 'optional'. Most will skip the appetiser in search of the meat.
In this circumstance you cannot equate movies with books. People with cite the Star Wars prologue as a defence but Star Wars is a film to be VIEWED. The prologue is one of the few occasions where the customer is required to READ. If they'd wanted to read they'd have stayed at home with a good book and not ventured out to the theatre.
The only reason for an infodump is if the information cannot be revealed via a scene.
You can move the "infodump" out of the main narrative, and include it as reference material in the front-matter or appendices.
For example, instead of your MC reciting the list of important events leading to the start of the story, include these in a timeline at the front of the book.
The reader will not read it before they start, but they will refer back to it as events are mentioned in the text. Or you can use a footnote to suggest a reader refer to it.
Likewise with maps, geneologies, Dramatis Personae, etc.
NB: historical novelists have the same problem and handle it (I think) slightly better than fantasy writers. CJ Sansom's "Shardlake" series and Colleen McCullough's "Masters of Rome" are good examples to follow.