still not starting

I had mine not launching either and found out about screen resolution not matching the resolution in AC unity. I had min as custom (NVIDIA scaling). When I switch back my resolution to a standard one, it fired up.
My guess is that you need to mirror the setting of AC unity to have the first time launch and after you're done you can change it
Some report having two keyboard or some extra controller or anything else that is not a "standard typical" set up, need to be remove to initate the first launch. After you launch it once, then you can plug back or go back to your special setup and it will launch from now on.

my game doesn't even show in my uplay

When I attempted to play this game it wouldn't even work since I cant get past the initial old ubisoft launcher

Thank you @Staticuss! This was my problem, it took some time to find this post again, funny that it was in the top when I had just bought the game and was about to refund it.

i could not even launch it in the first place, the servers at ubisoft are bad :(

L

if you have over 24 logical cores (amd, ryzen, threadripper 3960x) launch msconfig from "run" click over to boot> advanced optionss>and select "12 " number of processors ( reboot). i have to do this when i want to play unity . when i want to use all my cores (48) i launch msconfig again and select normal boot up (restart) and i get to use all my cores again.

playing on linux never face this problem

I finally found a solution to the problem, thank you very much