Sims 4 won't repair or update

@lil_mystri  If you use a third-party antivirus, disable it temporarily, then clear the App's cache again and try to repair.

If that doesn't help, do you have fast-enough internet that reinstalling the game wouldn't be a burden?  If so, please try that.  But instead of uninstalling Sims 4, rename the folder that contains the game's program files.  It's in the location you see in the EA App, under Sims 4 > Manage > View properties.  This will make the App think the game is uninstalled.  Be sure to close the App and kill the EABackgroundService in the Task Manager before renaming the folder.

Once you've done this, restart your computer.  Create a new folder on the root level of the drive of your choice, for example C:\Games is fine, but not C:\Program Files\Games.  This is where you'll install Sims 4.  Open the EA App, click Sims 4, then Install, and you'll be asked where you want the game.  Choose the new folder, and let me know how far the process gets.

If your internet is slow, you can try the same, except once you've started the download, pause it, then copy over the files from the previous install into the new location.  Once you resume the download, the App should verify the files' presence, download anything missing (e.g. the update content), and finish the install.  Hopefully.