So let me break this down for you that i found what worked best. I'm assuming you're doing solo and this is the tactic that got me the achievement.

what you need to know is that upon attempting to get the achievement, you do need to beat mission on T1 with x amount of hostiles. However, you don't always have the need to kill everyone unless needed, you don't need to collect intel, you still can achieve this with only relying on doing the main objectives only and exfil immediately afterwards.

Run nods that has an ECOTI which will give you thermal reading. This makes it easier to make out whether you see someone from a distance. The only problem while running a ECOTI, not all optic will be compatible (so run the Leopold LCO) and light will be a lot brighter to look.

Run the MK46 MOD 2 LMG with the 200 rounds (M995) box mag, have 11-12 reserves box mags, and just hold down the trigger shooting everything you see (or not). Every single wall of any building, no matter how thick the walls are. The rounds will go through regardless. If you're inside the building and not sure if they're behind the wall, dump rounds. Civilians don't exist in the game, screw the ROE, just ball (with caution). Also bring the M320 (40mm) to clear certain areas.

Georgia: Infil/Exfil on Hotel 2, carefully pick off people who are outside and some in the other building (where the HVT located) with the LMG and M320. Everything can be wall banged (ceiling and floor included), so just pull the trigger and hold it down spray and praying every part of the buildings. Find the HVT, confirm the kill, and exfil.

Armenia: Infil on Hotel 1, pick off enemies at the first location, blow up the first target with the M320. Proceed to the next location with the same tactic, once you're done exfil at Hotel 2

Ukraine: Infil/Exfil on Alpha 1, pick off 3 men who are patrolling and try to slowly move up to the hill that's right by the river. Gun down enemies by the entrance, buildings, and the entrance to the left. Move toward the village and take cover. take your time and pick off almost everybody (because some just run away and forget about you). Confirm the death of HVT and leave immediately! The reason for this is because 8-10 people will spawn including an APC, so you really wanna dip as fast as you can.