I also did what the post said only I used the Alderlake workaround. My computer setup is very similar to Shadyn's.
I was able to get the game to work several days ago then added BitDefender. I have tried running with exceptions on the executables and all of the EA folders (see attached image). I have zero custom content, I do have every expansion, etc. I have also tried shutting BitDefender off completely. I make sure I am logged out of the EA App and that it is not running, I have killed the EA background app before running TS3.
My launcher will come up, but is blank on the right side (see attached image). When I hit play, it shuts down to the EA App with the following message "The Sims 3 is already running Go ahead and start playing. It's a good one." (see attached image) Yes, if I could actually play it.
Attached is my dxdiag and gyazos of my launcher window, the error message, and my Bitdefender exceptions.