Surely a predicament you've found yourself in! However, there's no need for panic. The FSX.CFG file should indeed exist after a fresh installation of Microsoft Flight Simulator X. It's a crucial configuration file, storing various settings related to your FSX setup (such as graphics, sound, and controller options). This file allows users to make advanced tweaks to optimize the simulator's performance or adjust settings that aren't available within the in-game menus (such as your mentioned autogen trees versus buildings).
Autogen, in this context, refers to the automatic generation of scenery and objects within the flight simulation environment. These can be things like buildings, vegetation, and other landscape elements that make the simulated world look and feel more real.
First things first, are you sure you're searching in the correct location? The FSX.CFG file isn't located in the main installation directory of FSX. Instead, it's typically located in your AppData folder. To clarify, AppData is a hidden folder in Windows where applications store user-specific data or settings.
Here is the default location of the FSX.CFG file:
C:\Users\YourUserName\AppData\Roaming\Microsoft\FSX
Replace 'YourUserName' with the username you use for your Windows profile.
Please note that the 'AppData' folder is hidden by default in Windows, so you may need to enable the display of hidden files and folders in your Windows Explorer settings before you can navigate to it.
Once you've located the FSX.CFG file, you can open it in a text editor like Notepad to make changes to the autogen settings. Look for a line that says 'TERRAIN_MAX_AUTOGEN_TREES_PER_CELL' and 'TERRAIN_MAX_AUTOGEN_BUILDINGS_PER_CELL'. These values will dictate the balance between autogen trees and buildings.
Regarding your question about Microsoft Flight Simulator (2020) and X-Plane 12, these newer platforms do have similar configuration files, but they are not as easily user-editable as the FSX.CFG file. It's usually recommended to make such adjustments via in-game settings or addons specifically designed for these platforms.
Remember to save your changes after editing the FSX.CFG file and then restart the simulator to ensure the changes take effect.
I hope that sorts things out for you. Keep us posted on your progress!