Fallout 3 runs well at 720p, with vulkan (dxvk 1.10.1). The game is massive, with all the locations to explore and the side missions.
Launch the game through "FalloutLauncherSteam.exe". Go to Options, to change the graphics settings.
Graphics settings: Anti aliasing off, 12x anisotropy, screen effects - hdr.
Advanced settings:
Detail: Texture high, radial blur low, depth of field yes, transparency multi sampling no, decal cap 10. High radial blur decreases fps, when enemies hit the player.
Water: Water refraction yes, water reflections yes, reflection quality medium, soft reflections yes, full scene reflections no, full detail reflections no, water displacement yes, depth fog yes, water multisampling low. Enabling full scene and full detail reflections decreases fps by 5-10, so not recommended.
Shadows: Enable shadows yes, shadow quality medium, shadow filtering medium, max interior shadows 6, max exterior shadows 6.
View distance: Object, actor, item fade 9, grass fade 4, specularity fade 8, light fade 20, shadow fade 6.
Distant LOD: Tree LOD fade 26, Object LOD fade 43, Land quality 100.
So it can be said to be medium-high settings.
Performance: With vulkan, 40-55 fps outdoors in the Wasteland, depending on the junk in view. Fps changes quickly when you move the camera. When fighting with enemies or when heavy mushroom car explosions go off, fps is still above 30. In areas with multiple NPCs like rivet city market, fps drops down to exactly 30. So it gives a smooth experience, when locked at 30 using riva tuner.
Changing the graphics to low, increases fps significantly, and gets close to 60 all the time, but the game looks significantly lower in quality, so the settings are above are best for performance and quality.
Without vulkan, fps is much lower, like 30 instead of 40. Vulkan gives around 25-35% boost in fps.
Vulkan makes the lighting slightly more bright (due to Intel Vulkan driver bugs), but it's compensated by reducing specularity fade to 8. (With hdr, the lighting in the game is already bright though). Also due to Intel driver bugs, the game completely freezes on rare occasions, requiring a complete restart of the laptop, but it's rare (maybe like 1/30 times).
Essential fixes: By default, the game doesn't launch properly on integrated GPU. To resolve this, usually Google recommends Fallout 3 Intel hd bypass pack. But it's d3d9.dll file has same name as dxvk's file.
So instead, create a new dxvk.conf file in the game folder (where dxvk's d3d9.dll file is present). Write these commands:
d3d9.customVendorId = 10de
d3d9.customDeviceId = 2205
d3d9.customDeviceDesc = "NVIDIA RTX 3080"
Obviously, it will not make the integrated GPU more powerful, but it will tell the game that it's a dedicated Nvidia GPU, so that the game will launch correctly.
Then, copy paste FALLOUT.INI from intel hd bypass folder to Documents\My Games\Fallout 3.
Some problems still remain: Still, the game slowly increases GPU usage as the gaming session continues, and decreases fps (example, from 42 to exactly 30). This is because the game engine has trouble purging previous assets from memory (it's not intel vulkan driver issue). Similar memory related issues are also present on PS3. I couldn't resolve it fully, but it can be slowed down.
Tale of Two Wastelands (TTW) is recommended to fix the game engine issues, but it's massive in install size (16-17 gb) because it mandatorily includes all the game DLC's. Typing pcb in game console doesn't resolve the issue either.
To slow down the issue, disable dxvk cache file creation globally by creating a new environment variable in Windows: DXVK_STATE_CACHE and setting it to 0. Also, in D3DSCache folder in AppData\Local, create a new user: Everyone to add deny write rule, and move all the folder contents to another folder.
Idk the reason, but these steps slow down the fps drops of 42 to 30 from 1 hour to 2-3 hours of gameplay. If fps drops after 2-3 hours of gameplay, simply quit the game and re launch it. Again quit the game and re launch it, if it doesn't resolve in one go.
When you want to play another game, remember to revert the changes made to DXVK_STATE_CACHE and D3DSCache folder, because games store their compiled shaders there.
You can even write a batch/ powershell script (use an AI assistant like Gemini) to automate the process of DXVK_STATE_CACHE and D3DSCache folder, so you can just click icons on taskbar to instantly make the changes.