This issue with pixels swapping appears to be a bug with Nvidia drivers.
Described here by riperiperi. I set Vulkan/OpenGL present method to Prefer native for The Sims Legacy as he described and now it renders just like it did before I updated my drivers. You might want to try it, jnhmthw
Thanks so much Rakeeya. I first tried the 2nd patch as-is as it mentioned visual artefacts, but there was no change. I then did the NVIDIA control panel workaround as you suggested, which looks to have resolved the glitchy pixel swapping. Thanks!
Thanks for pointing out that article too - it's a great analysis of the graphics of the new release in general, and explains well the issues with high DPI scaling that I've been trying to speak to in this thread.
