OK, here are my own experiences with DX11 after short testing in CAS and live mode. In CAS, everything seemed to be OK. Even my CC seemed to be unaffected. In live mode, everything looked OK at first glance. However, FPS was very unstable even when nothing was moving, dropping between 65 and 75. In DX9, my FPS is pretty stable on 75 when camera is idle. Things, however, got worse the moment I moved the camera. Now, the framedrops were way more significant and I even got to 30 FPS when moving fast through the neighbourhood. Yes, it was raining, which may affect the performance, but it never was this bad for me even on my old graphics card (GTX 1050 Ti). Ever since I've got my current graphics card, RTX 3050 (8 GB variant), my FPS in Sims 4 were very stable and hardly ever dropped bellow 60, most of the time, they stayed between 70 and 75. On top of that, I also noticed small graphical glitch when trying to save the game (through Save as dialogue), when the screen became white for a few seconds. Never happened to me in DX9.
Plus, I think loading times are also longer in DX11 than they are in DX9. I did not measure it, but it sure seemed that way to me.
My PC is:
Ryzen 5 5600X
RTX 3050 8GB; NVidia driver version 555.85
32 MB RAM.
Windows 11 23H2
I may post full DXDiag if you want, but I think this should be sufficient info.
One thing is clear, though, I am staying with DX9 for now.