u/Azimovikh

To explain everything? Uh . . . That would be bothersome. Buuuut. Eh. But tl;dr.

• Comfortably go through; Usually low-to-mid fantasy settings where magic is rare, weak, or poorly scaled for large-scale warfare. The fantasy side generally lacks the raw destructive power, numbers, or versatility to counter modern combined arms doctrine (air superiority, artillery, drones, logistics, etc.). They're pretty much basically medieval/renaissance worlds, so, for examples; In A Song of Ice and Fire, magic is extremely rare and subtle. Lord of the Rings has powerful individuals but very little battlefield magic, GATE's magic are near-featless, Goblin Slayer and Frieren has powerful mages but most of their feats are counterable with modern logistics and tactics.
• Some hiccups; These worlds have more dangerous magic, monsters, or special abilities that can cause real trouble locally, but they still lack the consistent scale, coordination, or countermeasures to stop a determined modern military. Modern forces would suffer casualties and need smart tactics, but ultimately prevail through superior range, mobility, industrial capacity, and the capability to adapt. For examples, Faerun has plenty of wizards and monsters with weird hax, but most threats are regional and not prepared for cruise missiles, stealth bombers, sensors, beyond-reaction-time logistics, and reverse-engineering their weaknesses. Oh, and Gond's ban of gunpowder, the original smokeless powder is chemically distinct enough from modern gunpowder, so. Anyways. Avatar bending is flashy and powerful individually, but benders can be outranged and overwhelmed by artillery and machine guns. Fullmetal Alchemist and Elder Scrolls (Skyrim-era) feature strong magic and alchemy, yet still fall short of matching modern military saturation firepower and air dominance. Ivalice has some industrialization and magic shenanigans, but does not have the weird hax and weirdness DnD has.
• Without clear counters; These settings contain high-magic elements, exotic abilities, or industrialized magic that create serious problems modern militaries have no easy answer for. While modern forces could still win battles, the fantasy side has tools (massive area-effect magic, teleportation, magical technology, reality-bending phenomena) that could inflict devastating losses or force a messy stalemate, and different than the previous tier, this one tier actually can use them effectively on a large scale. For examples, Stormlight archives with their surgebinding and shardplate. Eberron features widespread magic and magitech, and a level of social and technological advancement that's industrializd and given the scientific method to use DnD's shenanigans on a more mass scale. Golarion has more setting-widespread and more magic focus that defies your typical logic.
• We're fucked; These are high-chaos or overwhelmingly powerful settings where the baseline threats, magic systems, or metaphysical rules are so extreme that conventional modern military forces would be rapidly overrun or rendered irrelevant. The fantasy world has too much raw power, corruption, or existential weirdness for guns and bombs to solve. Warhammer fantasy's Chaos, raw usage of insane magic, daemonic powers, get that way. Planescape has sheer conceptual hax and insanity from the infinite planes with a lot of them exploiting magic for their techniques. Shadowrun has both the tricks of modern world combined with insane magic, so. Yeah.

Note : The stuff I made it on is based on vibes and the things that exist in the setting in general, the scale of magic, how common it is, how much fantasy there is and what the world in general has.

Outliers (for example, deities in general, Sauron from Lord of the Rings, Faerun's legendary and epic characters [level 21+], Dragonborn and Daedra from Elder Scrolls, Agarthans from Fire Emblem Fodlan, Daelkyr from Eberron), are not counted. They qualify as an outlier if they get the weirder shenanigans and can do shit that otherwise won't make it in setting as a normal thing or as background cosmic threats.