First let's list the achievements that won't unlock in the current version of the game and why:
- Dorifto-samurai: buggy implementation
- Car owner: server offline
- Germans do things: server offline
- Undecided: server offline
- Drift king: buggy implementation
- Collector: server offline
- Success: unimplemented and hidden, description once unlocked says buy all cars and upgrade them to stage 5, mod changes it to buying the Skyline R34
- Experienced drifter: buggy implementation
- Geometry: unimplemented and hidden, description once unlocked says do a 360 in drift, mod changes it to buying the Skyline R32

Download Assembly-CSharp.dll from https://drive.google.com/file/d/1ERoA0a71gW9EMm1NZZZxh_AFbLtFKTS3/view?usp=sharing
and copy it to Steam\steamapps\common\CrashMetal\CrashMetal_Data\Managed overwriting the existing file.

Start the game after copying the file and it will fix the servers offline and buggy achievements.

And remember to buy an R32 and an R34 to get Geometry and Success.