Try moving your Sims 4 folder (Documents > Electronic Arts > Sims 4) to your desktop. No, do not delete it as that is where all your saved games are and you will want them later. Next start up Sims 4. Basically, this is like doing a factory restart on the game that allows the files to regenerate in case something has become corrupt. Go ahead and start a new game just to see if the game works and you aren't still having issues with the game itself. Play for about an hour just to test drive and see if there are any other errors that occur. If everything starts up ok, then it is probably one of your Mods or CC that is now conflicting with the updates and you should check those sites to see if the mods have been updated to work with the latest patch. If the mods or CC is not updated, you may have to play without those.
So it did start up normally but now everything I've done is gone and none of the mods aren't there. How do I get it to return to normal?? Thanks!
Edit: Also things I've saved to the gallery is gone ☹️
Your Mods are in the folder on your Desktop, as are your saved games and CC. Since you said the game worked again, it leads me to believe that one of your Mods or pieces of your CC is out of date due to recent updates. Check the sites that you have downloaded your Mods and CC from and check to see if the Mods/CC have been updated to work with the current updates. You should turn off Automatic Updates in Origin so that you can check to make sure your Mods are updated to the latest patches before you update.
Before adding everything back into your game, you should add only a few pieces back at a time and see what may be causing your game to not start up.
