Just search for CUDA_NVRTC_ENABLED inside the provided OptiX SDK CMakeList.txt files, not inside your build folder which already generated the solution with that setting.
Find this CMake set() instruction:
# Select whether to use NVRTC or NVCC to generate PTX
set(CUDA_NVRTC_ENABLED ON CACHE BOOL "Use NVRTC to compile PTX at run-time instead of NVCC at build-time")
and change the default value from ON to OFF.
Then delete the CMake cache and generate the solution again.