mkdir build && cd build && cmake .. -G "NMake Makefiles" -DCMAKE_INSTALL_PREFIX=C:\kderoot -DCMAKE_BUILD_TYPE=release -DCMAKE_PREFIX_PATH=C:\kderoot;C:\Qt\6.3.0\msvc2019_64;C:\Dev\Swerve\thirdparty\karchive\zlib;C:\Dev\Swerve\thirdparty\karchive\bzip2;C:\Dev\Swerve\thirdparty\karchive\libLZMA -DQT_MAJOR_VERSION=6

Output:

CMake Error at C:/kderoot/share/ECM/kde-modules/KDEInstallDirs6.cmake:200 (find_package):
  Could not find a configuration file for package "Qt6" that is compatible
  with requested version "".

  The following configuration files were considered but not accepted:

    C:/Qt/6.3.0/msvc2019_64/lib/cmake/Qt6/Qt6Config.cmake, version: 6.3.0 (64bit)

Call Stack (most recent call first):
  C:/kderoot/share/ECM/kde-modules/KDEInstallDirs.cmake:15 (include)
  CMakeLists.txt:14 (include)


-- Configuring incomplete, errors occurred!
See also "C:/Dev/Swerve/thirdparty/karchive/build/CMakeFiles/CMakeOutput.log".

The Qt5 build with 5.15.2 is fine, but naturally, I want to build with Qt6.

Any ideas?

Using Quazip anyway so this is not a massive priority, but keen to try out karchive if possible.