The possible reason why the vray toon option is not available in the atmosphere effects section could be that the V-Ray version you installed does not include the vray toon feature. Please make sure you have installed the correct version and check if your V-Ray license includes the vray toon feature. If you confirmed that you have the correct version and the license includes the feature, but still cannot find the vray toon option, try reinstalling or updating the V-Ray software. If the issue persists, it is recommended to contact the official technical support team of V-Ray for further assistance.