It's kind of odd that it's able to find `BoostConfig.cmake` in this scenario, since it shouldn't consider `\tools` folder to find `BoostConfig.cmake`, since `tools` is not the standard path that `find_package` would add to `C:\boost_1_88_0`. So there must be also `C:\boost_1_88_0\tools` somewhere on the PATH, allowing it to find `BoostConfig.cmake`. Either way, I believe it's not the correct way to provide boost config to cmake. The correct way is to set `Boost_ROOT` (or `BOOST_ROOT`) to the boost installation directory - typically `C:\boost_1_88_0\stage`, that would have `lib\cmake\Boost-1.86.0\BoostConfig.cmake` that cmake would be able to find. Note that you don't need to set `BOOST_ROOT` explicitly, it's just one of the options to add it to the path - you can also add `C:\boost_1_88_0\stage` to the general `CMAKE_PREFIX_PATH`. If you still have issues, please provide a minimal cmake file to reproduce this - it's very important to know what cmake version requirements are used in the file and what policies are set.