Constant lags despite high end PC.

Rabbitypo​  Your dxdiag lists a few crashes of the graphics driver, so please do a clean uninstall and reinstall of the driver.  Here's how:

https://crinrict.com/blog/2019/02/clean-re-install-of-graphics-drivers-with-display-driver-uninstaller-ddu.html

The fact that the game is smooth in a new save and choppy in an old one can have a number of causes, anything from too many objects on the lot to the green Eco footprint.  The post I linked earlier about changing values in GraphicsRules.sgr can help with the former; for the latter, try disabling the Eco footprint.

If neither helps, move your main household to a new, blank or EA-made lot, and see what happens.  You don't need to save your progress.

Francoisf30​  I'm trying to help here.  I could go into the reasons why testing a new save is relevant, and I listed a couple of them above, but the point is that it's important to find out whether the problem is contained to one save or not.  Even if it's a fundamental change in the game, it matters what that change was, where and when it's present, etc.

Your thread was moved out of bugs because performance issues are considered system-side issues until proven otherwise.  Most of them do turn out to be on the system or user side.  Even when they're not, the people who work for EA (I am not one of them) will want to know that the player has eliminated hardware and other software as potential causes before looking into it.