Re: Origin error: unable to start due to missing game data. Install Legacy Edition
@SnarkyWitch A couple months ago, a few people with Avast reported the same error message as you had, with Avast installed. It turned out that they didn't have TS4_x64.exe, despite having been able to play the game before and despite having set exceptions for it and Origin in Avast. I'm not sure exactly which setting was at fault, but the only solution was reinstalling while Avast was totally disabled.
You can try clearing Origin's cache and repairing with Avast disabled, but if that doesn't help, then it might be necessary to uninstall and reinstall with Avast disabled. You could of course try just with the exceptions set, but that didn't work for the first affected players. If you want to save time when reinstalling, you can also just install the base game; if the exception doesn't help, uninstall and reinstall again with Avast disabled and see what happens.
And yes, TS4.exe is from the Legacy Edition. Everyone has it regardless of whether the LE is installed; there are additional files that make the LE work that you wouldn't have installed, or else Origin would just run the LE without prompting you to download it.