It apparently prevents a location from showing up on any kind of map. It literally can't be mapped.
Which means pretty much all modern guided weapons are useless.
Of course, that is only one of the many defenses that need to be overcome.
I mean muggle aversion charms are a thing. A muggle literally can't go to Hogwarts. Attempt to do so and they will see only a ruin that they become utterly convinced isn't safe, or isn't interesting, or that their kid is locked in the car and they have to save them, or whatever.
Short of a magic counter for those kinds of passive defenses, muggle infantry is entirely worthless against Hogwarts as they will always convince themselves that they need to be somewhere else. And given that muggles all see it as a ruin already, and that the charm apparently works with their own minds to provide an excuse that they find acceptable, you may well have the muggle attackers convinced that they already attacked and destroyed it.
But ultimately, all of this already assumes that you are negating virtually all of the wizards advantages. To reach the point where a dude with a gun is fighting a dude with a wand at ten paces is to essentially word of god fiat your way past 90%+ of the wizards capabilities.
And wizards deciding that they need to be serious? Well then the muggles are thoroughly fucked even in direct combat.
Step 1: Make an invisibility unitard.
Step 2: Charm it with Cushioning, Unbreakable, and Silencing charms.
Step 3: Cast the Bubblehead and Supersensory Charms.
Step 4: Put on hearing protection.
Step 5: Walk through virtually any muggle facility in the world carrying an adult mandrake. Watch everyone who hears it instantly fall over dead.
But really, step five can be pretty much anything because your wizard is pretty much utterly immune to any muggle response.
Unbreakable does exactly what the name implies, it makes something unbreakable. Cast it on a shirt and suddenly that shirt is bulletproof. Pair with a cushioning charm to negate the kinetic energy component and you get to walk around immune to bullets and shrapnel and blades.
The Bubblehead charm provides immunity to inhalation vector gas weapons, and modifying it for full body protection from chemical weapons is probably not that difficult.
Supersensory Charm means that the wizard isn't ever surprised or ambushed.
Invisibility cloak (in the form of the unitard) makes them impossible to see while the silencing charms make them completely silent. Thermal imaging and IR might still work (assuming that magic can't solve those issues relatively easily).
Now who is wearing that suit? Someone who can teleport, unlock any door, turn structural supports into lions, burn down cities, etc.
And now the real kicker, you don't actually need that many of that wizard. A time turner means that they can attack one place, jump back in time and attack another, jump back in time and attack a third, etc.
But lets say that you do manage to attack Hogwarts or the Ministry or Diagon Alley, etc. How are you finding Malfoy Manor? Shell Cottage? The Burrow? Number 12?
A hundred thousand wizards showed up at the Quidditch World Cup. All attacking Hogwarts is going to get you is to enrage the wizards as the muggles just attacked their children and tried to carry out the Witch Hunts again.
Each and every one of those adult wizards is a potential person of mass destruction. Apparate into a city, cast Fiendfyre (if Goyle can do it, it can't be that hard), apparate away and watch the city burn with unquenchable hellfire.
Grindelwald was going to burn Paris down with a spell that wouldn't affect those who were loyal to him. Do you doubt that such a spell couldn't be modified into one that wouldn't affect those who were magical?
Then there are the beasts. Dementors show up at a military base and suddenly everyone present is seeing their worst memories and shivering, all the while flight capable demons that they can't even see (and are immune to most anything they could try) are going around and eating their souls. Let a Nundu loose in London and suddenly they are left with nuking the place or being the epicenter of every plague. Then there is the bird whose cry drives anyone who hears it mad; just put a few under the Imperius curse and have them fly around squawking - you now have a few hundred thousand insane people to deal with.
Now while all this is going on, remember that the muggles no longer have electricity. Why? Because wizards walked around turning power transformers into lemon-pops.
There are no more bridges? Why? Because wizards teleported around and casually transfigured their support beams into metal/stone/concrete lions that are now rampaging through muggle cities killing everyone they come across.
You aren't ever going to get army vs. army combat.
