How to Survive 2

This achievement is broken in the latest version of the game but it is possible to get it by using an older version. You can revert your game to the old version by following these steps:

1. Download and install .NET 6
2. Download DepotDownloader from Github
3. Extract it to any folder
4. Open a CMD window and navigate to the folder
5. Run the following command
   dotnet DepotDownloader.dll -app 360170 -depot 360171 -manifest 6980166005766427148 -username #yoursteamusername#
6. Wait for the download to finish
7. Navigate to the downloaded game folders and overwrite your existing game folders (i.e. C:\Program Files (x86)\Steam\steamapps\common\How to Survive 2) with them (backup your save game before you do it if you want to be extra safe)

Now you can start the game via Steam and complete any holiday mission to get the achievement.
Keep in mind that you cannot play in online camps that were created with a different game version.

Thanks goes to Gemini & Mercury who figured this out first.