Intel Core i9-9960X is processor manufactured by Intel and launched in Q1 2019 . It's using FCLGA2066 socket. It has 16 cores and 32 threads with clock of 3.1 GHz that can turbo clock itself to 4.4 GHz . This processor is used in Desktop devices and can consume up to 165 watts of power .
NVIDIA GeForce GTX 1660 is graphic card manufactured by NVIDIA and launched in Q1 2019 . It's using PCIe 3.0 x16 bus type. It has core clock of 1530 MHz and 6144 MB (6GB) of memory . It supports DirectX 12 and OpenGL 4.5 . This graphic card is used in Desktop devices and can consume up to 120 watts of power .
This configuration has 31.1% of graphic card bottleneck .
When playing games your processor won't perform on maximum possible performances (won't be utilized to the maximum), because you graphic card cannot handle delivered data fast enough. This theoretically means that utilization of you graphic card will be on maximum and the potencial of processor will not be completely used.
Graphic card bottleneck is better, than processor bottleneck, because utilization of your graphic card will be on maximum and you will experience maximal performances that your graphic card offers. Also your processor can handle some other programs in background because it won't be maximally utilized.
You can resolve this by upgrading your graphic card or by downgrading your processor. Downgrading your processor doesn't make much sense and in that case is better to leave current processor in you computer, because you can run more background task that won't interupt your gaming experience.