Muggles would NOT steamroll the wizards (Harry Potter) in an all-out war. In fact, it's the opposite.

Every time this prompt comes up, people would fantasize about sniping a Death Eater with a .50 cal, taking down a dragon with an F-16, or just nuking Hogwarts. None of this would happen, because the wizards would never wage a conventional war against the muggles. A wizards' invasion is going to insidious and oppressive. They would fully utilize their magic to wage guerilla warfare, espionage, sabotage, misinformation, and every dirty trick available. There really is nothing we can do to counter teleportation, mind control, mind reading, shapeshifting, mass illusions, ethereal magical creatures, and minor time travel. They will dismantle every governing body and military forces. Finding them is an astronomical challenge, because they can create dwellings hidden in pocket dimensions. A bunch of wizards can create an Air BnB in the Pentagon briefing room and none would be the wiser. They also look and sound like us. They can use special charms to make muggles subconsciously ignore them. They can create rains that erase memories. We don't see them, but they always see us. People won't listen to their president anymore; soldiers would not follow orders. Because everything and everyone can be under the influence of magic.

This prompt also always gives the muggles all the advantages while nerfing the wizards' intelligence. It's true that an average wizard is stupid and ignorant, but so is your average muggle. If the muggles are unified and bloodlusted, then so are the wizards, including the muggle borns. What do you think happens when Dumbledore and Voldemort team up? What are the NAVY SEALS going to do against dementors? Can we create a vaccine for Dragon Pox if they resort to bioweapons? You really think that a death squat led by Hermione Granger chugging Liquid Luck and save scumming with the Time-Turner can't infiltrate and take over every nuclear submarine?

The only reason the muggles have not been taken over is because wizards never had any reason to. They were content with their way of life. Only Grindelwald and Voldemort had serious attempts at an invasion, but they were both stopped by other resisting wizards.