Here is the full list of all 20 Xenonauts 2 achievements.
Construct an additional base on the Geoscape.
Cause an enemy unit to fall unconscious.
Lose a soldier in a tactical combat mission.
Kill an alien in a tactical combat mission.
Win the campaign on Recruit difficulty or higher.
Win the campaign on Soldier difficulty or higher.
Win the campaign on Veteran difficulty or higher.
Win the campaign on Commander difficulty.
Capture the Cleaner facility.
Set foot upon the alien homeworld.
Equip a soldier with a Colossus Battlesuit.
Shoot down a Battleship UFO with an interceptor.
Shoot down a UFO with an interceptor.
Have an interceptor shoot down 20 UFOs.
Kill one of your own soldiers during a tactical combat mission.
Kill an alien with reaction fire during a tactical combat mission.
Kill an alien with an energy weapon.
Have a soldier with 20 alien kills.
Deploy a squad consisting entirely of Colonels on a tactical mission.
Have a soldier achieve the rank of Colonel.