Can't get NEW CMP0147 (BuildInParallel) to work

I’m generating projects for Visual Studio 2022.
I upgraded my CMake.exe to version 3.30.2.
Then I bumped my cmake_minimum_required to 3.30.
I also added cmake_policy(SET CMP0147 NEW) a couple of times into my top-level CMakeLists.txt.

I now expected that the BuildInParallel flag is set to true for all add_custom_command calls. However, there is exactly one, which is in the ZERO_CHECK project. Everything else does not use this flag.

Is there anything else that I’m missing? From the documentation it seems like just setting the policy to NEW should do the trick.

See policy docs here: https://cmake.org/cmake/help/latest/policy/CMP0147.html#policy:CMP0147
And release notes for 3.27 here: https://cmake.org/cmake/help/latest/release/3.27.html#other-changes

Use the Ninja generator if you want really parallel builds!