Kill 50 enemies at long distance.

The distance required for kills to count for this achievement is unknown, however, the range doesn't seem to be too far. The combat in Metro: Exodus is typically either stealth or close quarters so it's likely you will need to grind this achievement.

The best weapon for this is the Valve Sniper Rifle, which can be found in various places, but most notably during the Caspian level. After helping Giul at her lighthouse and fighting through all of the Spiders in the archives you will be told to go and meet Anna. She will give you three side missions to complete, one of which is to kill a sniper in a crane that you're shown via the binoculars. If you kill this sniper you can pick up his Valve and it is set up with a long range scope.

Once you have this you can then go and find a group of enemies to grind out kills on. There is a small encampment of enemies to the East of where you find this sniper rifle, on a kill above the ship that is also a side mission. Be as far away from these enemies as you can while still being able to see and shoot them, then make a quick save. Kill them all, making sure to check the achievement tracker so that you know you're far enough away for the kills to count, then reload the save and repeat as necessary.