As Fantastic Beasts: The Secrets of Dumbledore continues the franchise's trend of expanding the world of Harry Potter, it creates a big Voldemort plot hole in the process. The original Harry Potter series stayed fairly self-contained within the United Kingdom, as most of the stories occurred in or around Hogwarts. In contrast, the Fantastic Beasts prequels seek to incorporate the wider Wizarding World as Newt Scamander (Eddie Redmayne), Albus Dumbledore (Jude Law), and their allies travel the world - but it also raises some difficult questions for the Harry Potter movies.
The Secrets of Dumbledore explores Albus' past relationship with Gellert Grindelwald (Mads Mikkelsen) as the Dark Wizard grows in fame and followers. Gellert plans to rig the election for the next Supreme Mugwump to guarantee that he will be made the ruler of the entire Wizarding World - and almost succeeds despite the many wizards who come from all around the globe to vote against him. In this way, Fantastic Beasts 3 focuses more on Albus' attempts to thwart this plan than on fleshing out their governing system, as if the movie itself is uncomfortable with the far-reaching plot hole it is creating.
The original Harry Potter series did not indicate that any of these international witches and wizards — who are so adamantly opposed to Gellert Grindelwald's power grab in The Secrets of Dumbledore — did anything at all during Lord Voldemort's rise to power. Neither during the First Wizarding War nor during Voldemort's rampage in England during the main Harry Potter years did the Dark Wizard face any apparent international opposition. Voldemort caused a great deal of death and destruction twice. The first time, only Britain's Ministry of Magic and the Order of the Phoenix stood against him, and the second time, there wasn't even the Ministry. Although this International Confederation of Wizards was mentioned in Harry Potter, the governing body never seemed to possess any real power. However, Fantastic Beasts 3 suggests that they could have done something and instead chose to ignore the greatest Dark Wizard of all time twice - creating a huge plot hole for the Harry Potter franchise.
Of course, Voldemort predominantly operated in the shadows, which was how he managed to avoid the Ministry of Magic's involvement in his affairs for so long, but this secrecy does not explain the great deal of ignorance shown by the rest of the wizarding world during Harry Potter. When the Ministry publicly denounced Voldemort's return, Albus was dismissed from his position on the International Confederation for speaking out, but the version of the organization in Fantastic Beasts 3 would never have been so openly complacent.
As a result, it's a glaring plot hole that Harry Potter never even suggests how the Dark Wizard might have prevented international wizards from taking an interest in stopping him. Although wizards from far and wide are concerned about the possibility of Gellert Grindelwald gaining power in The Secrets of Dumbledore, their lack of concern years later implies that the remainder of the Wizarding World was content to let Britain suffer and fall as long as the destruction did not extend outside its borders.
By expanding worldbuilding in Harry Potter, Fantastic Beasts: The Secrets of Dumbledore has also introduced a big plot hole for the original series. Emphasizing such international cooperation in the prequels does not align with what took place during both of Lord Voldemort's attempted rises to power. Despite being an even bigger threat than Gellert Grindelwald, the international wizarding community never lifted a finger to stop him.