Modern warfare is about the fact that a man-portable weapon can kill someone in man-portable body armor.
In the short term, your shield can protect against someone using non-military weapons. If it is light enough to carry, military weapons will penetrate it.
The penetration distance of a newtonian impactor is proportional to the ratio of mass and the depth of the bullet. A bullet can easily be made to be pretty long and relatively dense; your shield basically has to be bullet dense and bullet deep to fully shield the person behind it; if you want to protect 1 m^2, and bullets are 0.5 cm^2 cross-section, it must weigh about 20000x what a bullet does (ignoring propellant).
A soldier carrying 100 bullets can carry heavier bullets than your shield can protect from, given the same carrying capacity. If you have an exoskelliton that lets you carry a heavy shield? They can have an exoskelliton that lets them carry and shoot bullets that go through the heavy shield.
The ground, sand bags, buildings and the like are things you don't have to carry. They can easily have huge effective depths and soak up weapons fire without having them to be man-portable.
In response, attackers can set up heavy weapons. Weapons that aren't man (or exo-suit) portable, require set up, and can in turn blast through the fortification you are hiding behind.
This results in a red queen's race. One solution (or local optima) is WW1 trench warfare, which was a stalemate because (in simplification) the attackers could win against the front lines, but couldn't carry heavy weapons to defend their advances. So you would (at huge cost) overrun the front lines, then you'd be destroyed in a counter attack (as the enemy heavy weapons are in place, and you don't have any on your side). And repeat.
WW1 trench warfare gets beaten by mechanized troops, heavy weapons, tanks, airplane support, and modern fire-and-cover tactics to exploit breakthroughs.
Nuclear weapons make a continent-wide battle seem unlikely; less extreme combat tends to be more mobile and less total. Modern fire-and-cover tactics using mechanized forces that the USA uses relies on real time intel and the availability of unlimited range unlimited firepower support.
Your light mechanized troops advance until they hit resistance, then fall back locally, call down the thunder, then continue. The troops are armored against much human-portable firearms (in their mechanized infantry devices). They become vulnerable against human-portable anti-armor weaponry and static explosives (IEDs).
In towns, especially with civilian population, this doesn't work. Now, an asymmetrical situation where attackers using exo-suits heavily enough armored to defeat enemy most small-arms fire could develop, making in-city fighting mirror desert storm.
This is half way between police action and military action; when you are attempting to kill the enemy, but not the person standing next to them.
So, if your world has a dominant military power, their troops might use exo-suits that are armored against small-caliber fire (hunting weapons etc) and carry heavier ballistic shields (which can soak AK-47 scale fire). They would in turn carry a mixture of anti-personnel, anti-suit and anti-armor weapons.
Anti-suit weapons would have the problem of blowing through buildings (causing collateral damage) and the ammo would be much heavier. Anti-personnel rounds would be much lighter and would be less likely to kill people a few km away. And anti-armor would a speciality weapon.
The shields would be used by SWAT teams and military involved in asymmetrical police action, where most of the enemy is armed with obsolete weapons only. In a symmetrical fight, the shields would be mostly useless and discarded, as anti-suit weaponry would blow through the shield.
A suit carrying an armor-grade shield would be ridiculously slow and could be taken out by flanking or using anti-armor weapons anyhow.
Armor-grade troops -- whatever the analogy of tanks -- would be immune to suit and personnel-grade weapons, resistant to anti-armor weapons, carry ridiculous cannons that can penetrate enemy armor reliably, and act as light mobile artillery.
The thing is, suits are probably a bad anti-personnel weapon at this stage. Light unmanned drones with anti-personnel weaponry would be cheaper and smaller than anything you could wrap around a human. Suit armor would basically scale with what is required to survive attacks by such drones (as even insurgents could probably build hunter-killer drones).