For some time now I have had a laptop that has a Nividia as well as an internal GPU and I have now noticed that only my internal one has to work, my 2, however, does not work. Is that because they are not the same GPU or do I have to set something special there?
The internal iGPU is used for minor tasks without a claim to performance. The NVIDIA is used when performance is required (this happens automatically). You can also set this in the Nvidia control panel when it should be used.
The pc automatically uses the GPU that is needed at the moment. If you don't have a game open or other graphically demanding programs, only the processor's own graphics are used to save energy.
If you have problems that it does not switch automatically you can select the program with a right click "Start with nvidia gpu"