I solved the problem using Avast. I opened Avast and went to the Protection section and then Quarantine. There, I saw that Avast was blocking the file "ts4_x64.exe", which I believe is the missing file that the app can't find anymore. To fix it, I clicked on the three dots next to the file and selected Restore and Add Exception (remember to add an exception so that Avast won't block the file again). This definitively solved my problem. The reason why repairing the EA app works for a while and then gives you an error again is because Avast keeps blocking the missing file every time it reloads.
I'm a PC player, and i have Avast. If you also have Avast, try this method. (The Sims 4 should work immediately after this, but to be sure, restart your PC before)
@imen19 ... You seem to be right...I can't verify because I uninstalled Avast along with any quarantined game files! Now I persistently get this launch failure now no matter what I do. So, before uninstalling and reinstalling my game again, I decided to let Steam verify my game files and sure enough it found 1 file missing (the ts4.exe file?). So,now I have my missing file back I can get the Sims to launch again. Thanks for this information, it seems to be the fix for Avast users.
Came to find out that my Antivirus was blocking my Sims File and it was being quarantined. I had to find it and restore it. Also put an acceptance.
