A humble, hardworking British author - a woman no less, struggling for acceptance in a quite distinctly patriarchal business - is sought after to approve a movie based on one of her books; one to which she is very personally attached. So she flies to America to try and protect her creation from being manhandled by the Hollywood studio boss in question, whom she regards (not without reason) as a notorious purveyor of crass consumerist junkfood culture who famously turns everything he touches into stuffed animals and theme park rides. They famously clash, but the fight is over before it's begun by virtue of her needing the money more desperately than he needed her book-rights. And though the final product indeed makes her wealthy and famous, she must live out her days being chiefly recognized for a version of her character that she personally despised.
For a few decades now, that's been the reigning counter-culture narrative of Mary Poppins author P.L. Travers and Walt Disney - surely the most overly-vilified not-great man of Golden Age Hollywood. He was, to be fair, a caricature of his own making: Walt turned himself into a secular saint for public consumption, a symbolic amalgam of "good old fashioned Americana" to better convince a willing public that his cartoons, theme parks and merchandise wasn't so much being churned out by assembly-line but rather willed into existence by a jolly wizard in a tailored suit.
So when subsequent generations opted to turn against (however briefly or disingenuously) the "plastic" consumer sentimentalism he so embodied; it was only natural that the he'd be re-remade into something of a straw-Satan - a handy metaphor for everything "phony" and secretly sick about the ideals he packaged and sold. Despite what you may have heard, he wasn't a Nazi sympathizer, or even notably more racist or sexist than any other average white man of his era. Even accusations of anti-Semitism tend to be over-sold (though by no means excusable) by virtue of his opting to do business in the ONE American industry where a casual suspicion of Jewish persons wasn't considered commonplace.
By all reliable accounts, the truth is more mundane than shocking or edifying: He was a typical Hollywood mogul, simply one whose common flaws and failings were amplified by their proximity to his whimsical mythic self - an ugly utterance from any other unctuous tycoon is expected, but from Uncle Walt it's scandalous... or useful, if you're looking for an icon to prop up as a symbol of everything wrong with middlebrow American entertainment. And so Walt Disney: Complicated Individual becomes Walt Disney: King Jerkface, and the not terribly unusual situation whereby the author of a book that becomes a classic movie doesn't care for said movie becomes the Legendary Saga of how a True Artist got stomped on by The Hollywood Machine - a tale told by cultural snobs to other cultural snobs for decades whenever Mary Poppins comes up.
So now that Walt Disney (the studio - Walt Disney himself passed away two years after Poppins was completed and was not, despite what you may have heard, cryogenically frozen) has produced a movie dramatizing the contentious collaborative sessions during which author P.L. Travers and the studio's in-house script and songwriting team worked to hammer out the screenplay (over which she'd been given final approval); it's become a gut-reaction among some to assume that it's a kind of reactionary historical-revisionism: A way to finally, once and for all, claim the story for Disney (in the personage of Tom "America" Hanks, no less!) and relegate Travers to a bit role in her own life.