Apparently, the Recruit difficulty cannot be used for the Knock Them Out With Kindness achievement - and possibly other global achievements.
Kudos to player Cairn.L for finding that out.

• Chloroformed enemies stay unconscious indefinitely, even outside of bushes (unless discovered ofc), making missions with the spy relatively easy.
  
  
• Mandatory kills do not void the achievement - this includes mission targets and the sniper at the start of mission 3 (haven't tested anything else).
  
  
• Accidental kills (usually caused by environmental interactions, like falling objects) do not DO void the achievement (since v1.4).
  
  
• Placing additional knocked-out targets into such accident zones does not void the achievement. This includes setups like turning electricity in water on/off - allowing for unlimited "accidental" kills (confirmed by player hannez).
  
  
• Apparently, driving over unconscious bodies also counts as "accidental" kills. Kudos to hannez.
  
  
• You can also let allied soldiers kill enemies. Kudos to Pup. - Unclear in v1.4
  
  
• However, shooting explosive barrels or tanks - even if the game considers it an accident (i.e., no alarm is triggered) - will void the achievement (tested once in mission 4).
  
  
• Also, throwing unconscious enemies down a ladder counts as a kill and voids the achievement. (Throw an enemy down a ladder by ctrl+click on a ladder while holding a body.) Kudos to Covenant (ESP).
  
  
• Using the airstrike in missions 6 and 10 does not void the achievement (even if it kills enemies). - Unclear in v1.4
  
  
• Botching the fire test in mission 13 does not void the achievement (even if enemies die). - Unclear in v1.4
  
  
• Mission 14 ends immediately after killing the target - you can use this to your advantage.

• With the exception of the first mission (details below), you need to eliminate all enemies, likely including destroying enemy tanks.
  
  
• You can use accident kills to meet this requirement.
  
  
• You can also let allied soldiers kill enemies (tested in mission 5).
  
  
• Personally, I did not use the airstrikes in missions 6 and 10 or botch the weapon test in mission 13 to kill anyone. I either avoided those entirely or ensured all affected enemies were killed beforehand. I'm unsure if using them counts toward the achievement - can someone confirm?
  
  
• Regarding the first mission (tested in version 1.1 and 1.2)
  
  • After defeating the initial 3 Germans, a shootout occurs between 3 Brits and 8 Germans. You do not need to kill these enemies.
    
    
  • After the tank is revealed, you’ll cross a rooftop, beneath which is another shootout between 1 Brit and 3 Germans. You only need to eliminate the single German here, which can be killed via an accident kill.
  
  
• This bug from mission 5 has been fixed - the following section is kept "just in case".
  The flag in mission 5 wouldn't update to true for me, even after killing everyone and completing the mission. What helped, for some reason, was freeing the captain only after the map was cleared. (Possibly some enemies disappear after that cutscene? No idea. Bug report sent.)
  Kudos to Pup for suggesting that.
  Other players confirmed experiencing the same issue - with same solution.

• This bug has been fixed in version 1.3 - this whole section is kept here "just in case".
  
  
• Some players encounter a bug where the achievement "If the World Were a Village" becomes unobtainable. This is likely due to an incorrect value in the global save file (see Tracking Method sections). This persists in version 1.2.
  
  
• Details:
  There is a variable bCanGlobalAlarmBeSetOff in the global save file that should be set to false for mission 1, since it’s not possible to trigger a global alarm there. Unfortunately, for some players, the value is incorrectly set to true, which likely prevents the achievement from unlocking.
  
  
• Fix:
  For those willing to edit savegame files.
  
  
  • Exit game.
    
    
  • Find file "%LocalAppData%\Commandos\Saved\SaveGames\StatTrackingGlobal.sav".
    
    
  • Open the file in hex-editor (e.g. https://hexed.it/).
    
    
  • Change the value of bCanGlobalAlarmBeSetOff to false for the first mission (see Tracking Method sections for more information).
    
    
    • Locate string "BritishCompound" which starts a section related to the 1st mission (next mission is "Weatherstation", don't scroll that far).
      
      
    • In this section, locate the variable "bCanGlobalAlarmBeSetOff".
      
      
    • Immediately after it will be some spaces, "BoolProperty", some spaces and "10 16".
      
      
    • Change the "10" to "00".
    
    
  • Start the game and finish any mission. (Possibly a mission with global alarm count at least 1.) You can load an old save.
    
    
  • Of course, the achievement conditions have to be met, i.e. all the missions (except the 1st) have to be completed with global alarm count at least 1. You can use Tracking Method sections to confirm that.
    
    
  • You can fix this value anytime.

To automate the progress tracking process

• player Pup created a PowerShell code. You can check it out here:
  https://github.com/pmgledhill102/commandos-achievements-script/tree/main
  
  
• player Hannsen created a .NET code. You can check it out here:
  https://github.com/HannesHold/Commandos.StatTrackingGlobalParser

Find file
%LOCALAPPDATA%\Commandos\Saved\SaveGames\StatTrackingGlobal.sav
and open it in some hex editor (say https://hexed.it/).

After a bit you'll find a label of each mission followed by some variables. You are interested in 3 variables, each followed by a short string with clearly distinguishable true/false state:

• bWereAllEnemiesKilled BoolProperty
  
  • 00 12 = no
    
  • 10 12 = yes
• bWasNoEnemyKilled BoolProperty
  
  • 00 18 = no
    
  • 10 18 = yes
• bWasGlobalAlarmSetOff BoolProperty
  
  • 00 15 = no
    
  • 10 15 = yes

10 being the important part, the other number is likely just an identifier.

Example of mission 1 (BritishCompound) and bWereAllEnemiesKilled being true (you'd see a 00 before the 12 if it were false):

The mission labels are in order:
1. BritishCompound
2. Weatherstation
3. FortCapuzzo1
4. TrainBridge
5. Lighthouse
6. ChannelIslands
7. GermanMine
8. Lofoten
9. Harbour
10. GermanAirfield
11. GermanCompound
12. HeavyWater
13. SondergeschutzDora
14. OccupiedCastle