Massive lag / low FPS on high end PC

@danikeijzers  Is there a reason you're running the Legacy Edition of Sims 4?  Your dxdiag shows that you weren't before but are now.  Please switch back in Origin: open your game library, right-click on the Sims 4 icon, select Game Properties > Advanced Launch Options, and choose 64-bit from the dropdown menu.  If you don't see the option, repair the game first—the option is in the same right-click menu—and look again.

If you still can't play in 64-bit, let me know, and if you get an error when trying to switch, please post a screenshot.

Please also let me know what antivirus you use, if any.

Finally, if you can play in 64-bit but still see low framerates, please move the entire Sims 4 folder out of Documents\Electronic Arts and onto your desktop.  When you launch the game, a clean folder will spawn with no content.  (Your saves and other content will be intact in the folder you've moved but temporarily not read by the game.)  Don't add anything to the new folder yet; just start a new save and let me know how it runs.

You don't need to test while your computer is offline, at least not right now, but I'd suggest at least putting Origin in offline mode.