The next version of macOS called Mojave will only run 64bit apps, and both the App Store and Steam versions are 32bit.

I tweeted Aspyr and asked if they will be updating COD Black Ops and they responded with this:

@jzaret Indeed! We've got quite a bit of work ahead of us for our full list: https://blog.aspyr.com/2018/02/22/not-optimized-alert-macos-10-13-4/ We'll be gathering info to update this article as Apple releases more details throughout WWDC

thanks for info pish!