@KatAnubis The issue only affects newer Intel processors, so if you have an older one, or anything from AMD, you would be unaffected. My originally-fancy-but-now-a-bit-old CPU wasn't affected either, and frankly, no one really needs a current high-end model just for Sims 3. But that extra power is nice to have for (mild) futureproofing if nothing else.
@Qkaender Sims 3 has always required DirectX 9, which is separate from DirectX 12 and can be installed on a DX12 machine. DX9 was current when the game went into development, and there was apparently no reason to update to a newer version later. DX12 does not include DX9, so its presence isn't sufficient to make Sims 3 work. .NET Framework 3.5 includes 2.0 and 3.0, which .NET 4.x does not, so it's also been required for Sims 3 since 3.5 was released.
I don't know why you saw the message about .NET 3.5, since you should have already had it installed if you were ever able to play on this computer. But the important thing is that the game is working now.
