The “Earh 999999999” achievement is still bugged as on 2023-12-26. There is a guide on how to get it by Malkavian1331. Here is another (yet simpler) way to get the achievement.
How to Do
- Download the Assembly-CSharp [drive.google.com].
- Go to the game directory: SteamLibrary\steamapps\common\OnlyFap Simulator Deluxe
\Click & ♥♥♥ 
_Data\Managed . - Replace the original Assembly-CSharp.dll with the downloaded version.
- Now run the game. The achievement “Earh 999999999” should pop up once you have money >= 999999999. You can start from a save.
What Changed?
The developer seems to put an extra space at the end of the achievement name. I just removed it.
Before (note the extra space on line 16):
After:
How to Revert?
There is no need to revert unless the game has major updates after 2023-12-26.
To revert, right click on the game item in your steam library, and select Properties… -> Installed Files -> Verify integrity of game files .
I am very grateful for this information, friend.