Have you tried to reinstall or uninstall the game?
just about everyone has tried this, and despite reinstalling the game (for many, redownloading all 25+GB of it) the game continues to crash on startup.
I played this game through for about 2 1/2 months, beat it, then decided to play again for prestige after about 1 year after I last played it. No dice. Tried every suggestion from Ubisoft, other gamers, etc. Nothing works. tried both with current patches and with fresh install no patching. Same result.