I'll explain what I did below, before making any change please back up relevant files and make sure you have a decent computer (or at least a good video card, mine is Nividia RTX 2060 6GB). This method was initially posted by Foul Play in Discord, so a big thanks to them!!!
📢Check out the comment section first please. There seems to be some issues with Reshade/Gshade📢
We all know that The Sims 3 is a 32-bit old game that can only use less than 4GB of RAM, making it prone to crash due to memory overflow. Moreover, the game loads some texture memory into RAM, resulting in high RAM usage and low VRAM usage. Even the most powerful computers can't leverage their advantages. Therefore, what we need to do is to allow the game to fully utilize the performance of modern computers, while reducing RAM usage and increasing VRAM usage.
Download and install dxvk. Copy the d3d9.dll from the x32 folder to your bin folder (where you installed smooth patch and reshade/gshade). If you are not familiar with dxvk, it is recommended to check out this post (the 7th page) or videos about dxvk on Youtube.
If you have installed reshade/gshade before, you may be prompted to overwrite files, please choose yes. If reshade/gshade stops working after entering the game, reinstall reshade/gshade, and choose Vulkan mode(for reshade) /dxvk mode(for gshade) instead of d3d9 when installing. For GShade users: you have to manually delete the dxgi.dll generated in your Sims 3 bin folder after installing since it's unnecessary for a d3d9 game like the Sims 3.
Download the dxvk.conf file and place it in the same folder. Open this file with Notepad, delete all content, and add the following text. The first line must be added, and the second and third lines are used to set vertical synchronization and frame rate lock (It's just my personal preference, you can set it up based on the documentation on GitHub).
d3d9.textureMemory = 1
d3d9.presentInterval = 1
d3d9.maxFrameRate = 75
At this point, you can enter the game and observe if a TS3W.dxvk-cache file is generated in the bin folder. If so, dxvk is successfully installed. After entering the SIMS 3, the game settings will be reset, so you need to back up the original settings or readjust them directly. For me, simply installing dxvk converted the game's RAM usage of over 300MB to VRAM usage. The Sims 3 became more stable. It's harder for it to reach 3.7GB RAM usage and then crash.
(Experimental, set it cautiously and test yourself)Next, open your GraphicsRules.sgr, search and find two lines seti MemCacheBudgetValue, which determine the size of the game's VRAM Cache. The values behind represent 200MB (209715200) and 160MB (167772160) respectively. Modify these two values to larger numbers (for example 1073741824, which means 1GB). You can choose according to your computer and then have a test in the game. Check how much RAM and VRAM the game is using in the Task Manager after modification and find a proper value. If you don't install dxvk, increasing these values will make your RAM usage higher!
EDIT: The original values of 200MB and 160MB are calculated as 200x1024x1024=209175200 and 160x1024x1024=167772160.
I set MemCacheBudgetValue to -1 during testing, which represents no limit. Before using dxvk and modifying GraphicsRules.sgr, the game only used less than 1.5GB of VRAM. But now, the game is using over 5GB of VRAM after 2 sims day playing. However, RAM usage continues to increase at the same time and does not remain at a certain size as I expected. Maybe MemCacheBudgetValue should be set to an appropriate size to prevent the game from eventually using over 3.7GB+ of RAM.
After applying all these changes, with 6GB of mods and all graphics settings set to the highest, my game now runs more stable and smoother. I recommend you to try these steps above. Results may vary from person to person, so please share your test results in the comments^^
some extra information you may want to know
This method doesn't fundamentally solve the issue of the Sims 3. I suggest going through the performance optimization guides on Steam before attempting this.
Some of the settings in Nvidia (and maybe other cards) no longer take effect after installing dxvk. For example, the vertical sync, frame rate lock, and anisotropic filtering that I set in the Nvidia Control Panel don't work anymore. This may be due to switching the game from d3d9 to Vulkan. Fortunately, some settings can still be adjusted in the dxvk.conf file.
I recommend not opening the Nvidia Control Panel or similar utilities when running games with dxvk, as there's a chance it could switch the game back to d3d9 mode, causing the RAM usage to revert to its original state (I've experienced this a few times).
Each time you install and uninstall dxvk, switching the game between Vulkan and d3d9, is essentially making the game recognize the graphics card again, which results in the settings being repeatedly reset.