It seems you are looking in the installed folder by the screenshot you shared.
It sounds like your documents folder may have been moved to the D Drive? If that's the case, look for your Sims user folders via this path:
--- D:\Users\Username\Documents\Electronic Arts
Look for your Sims 3 user folder with this path:
D:\Users\Username\Documents\Electronic Arts\Sims 3
You will need to create a Mods folder and download the Resource.cfg file.
See the post linked below for more help on creating a New Mods Folder.
Sims 3 - Creating a Mods Folder/Installing Mods Step by Step Guide
https://www.carls-sims-4-guide.com/forum/index.php?topic=9187.0Look for your Sims 3 user folder with this path:
D:\Users\Username\Documents\Electronic Arts\Sims 4