I can't get shadows or directional lighting to work in Sims 3. This is a fresh installation of the base game on a fresh installation of Windows 10. (I own expansions but have not installed them yet.) No mods ever installed. There are some vague and blurry interior shadows, and vague, blurry shadows on trees very, very far away, but closer trees, walls outside, and objects outside cast no shadows, so everything looks flat. The sun is shining and it's 8 am, so I should think shadows should be visible. All graphics options are set to max within the game, and I've tried different resolutions. The graphics card is new and has the latest drivers. My specs:

CPU: Ryzen 9 3900 @ 3.8 GHz
GPU: Radeon RX 6900 XT, 16 GB
RAM: 32 GB, 3200 GHz

Initially the card wasn't found, but I googled for similar shadow issues and found about 5 tutorials that all said the same thing regarding changing / adding things in GraphicsCards and GraphicsRules. Two of those tutorials included files for GraphicsCards and GraphicsRules and DeviceConfig to overwrite. I tried it without those files, which didn't work, so I ended up using Carl's files. Now DeviceConfig lists the card as matched and found. Alas, this seems to have fixed others shadow issue, but not mine. The tutorials told me to add my card into GraphicsCards.sgr and GraphicsRules.sgr.

This is what the (I believe relevant) changes ended up being:

I ended up adding my card to GraphicsCards.sgr, like so:

vendor "ATI" 0x1002

card 0x1636 "AMD Ryzen 5 4500U"
card 0x6863 "AMD Vega FE"
card 0x15dd "AMD Vega"
card 0x687F "AMD Vega 64 and 56"
card 0x67df "Radeon RX 580"
card 0x73af "AMD Radeon RX 6900 XT"

In GraphicsRules.sgr I used this bit that every tutorial, and Carl's files, ended up changing:

include "GraphicsCards.sgr"
if (not $isCardFound)
set cardName $cardNameText
endif
setb textureMemorySizeOK true
if ($textureMemory == 0)
seti textureMemory 2048
# setb textureMemorySizeOK false

DeviceConfig appears to detect a find and match for my card now:

=== Application info ===
Name: Sims3
Version:
Build: Release
=== Rating info ===
GPU: 5 GPU Memory: 4 CPU: 4 RAM: 4 CPU Speed: 3793 Threading: 3
Adjusted CPU: 4658 RAM: 32710 Adjusted RAM: 32198 Cores: 24
=== Machine info ===
OS version: Windows 8 6.2.9200
OS prod type: 0
OS major ver: 6
OS minor ver: 2
OS SP major ver: 0
OS SP minor ver: 0
OS is 64Bit: 1
CPU: AuthenticAMD
Brand: AMD Ryzen 9 3900X 12-Core Processor
Family: 15
Model: 1
Cores: 24
HT: 0
x64: 0
Memory: 32710MB
Free memory: 28497MB
User: [redacted for privacy]
Computer: [redacted for privacy]
=== Graphics device info ===
Number: 0
Name (driver): AMD Radeon RX 6900 XT
Name (database): AMD Radeon RX 6900 XT [Found: 1, Matched: 1]
Vendor: ATI
Chipset: Vendor: 1002, Device: 73af, Board: 69051eae, Chipset: 00c0
Driver: aticfx32.dll, Version: 30.0.15002.1004, GUID: D7B71EE2-30EF-11CF-F27E-9F736FC2D335
Driver version: 1004
Monitor: \\.\DISPLAY1
Texture memory: 2048MB
Vertex program: 3.0
Pixel program: 3.0
Hardware TnL: 1

First of all, thank you very much for replying! I thought I had backed up the files but did not... I'll try the shading mod (because why not) then reinstall Sims 3 and try the tutorial you linked, which does seem to be a simpler version of the ones I followed. I seem to remember now that directional lighting was a feature of Sims 4! D'oh. I'm going to be embarrassed if it turns out that I've been tilting at windmills. I could swear this game had some kind of shadows outside, though? Are the following pictures what the game is supposed to look like? (They were taken at noon, as you suggested.) The interior lighting is gorgeous (even better than Sims 4) but there are no shadows for buildings, people, or close trees.

It's fixed!!! I reinstalled the game, and before I launched it for the first time, I followed the tutorial you linked and changed just the device code. Upon starting the game I did not receive an error about my graphics card not being found. All graphic settings were set to their lowest by default, which did mean there were no shadows. However, this time, after raising the shadows setting to the highest level, exiting the game, and then reloading, all of the shadows appeared! So that's it. Your first advice worked. Just change the device number, nothing else, and then make sure you set shadows to high and restart the game. This is such a relief. Thank you, you are fabulous!