VRS Feature test allows you to choose the rendering device and the display explicitly. By default it chooses a GPU that offers the highest VRS tier support (usually the dedicated GPU) and it prefers the display physically attached to an output on that GPU to ensure the highest possible performance.
On laptops with both integrated and dedicated GPUs, commonly the laptop display is physically connected to the integrated GPU to allow saving power by disabling the dedicated GPU when it is not needed. Any external monitors are commonly connected to ports that are physically connected to the dedicated GPU, so by default if you do have an external monitor, that monitor is used.
If you desire to run the test on the laptop display, you can change the display in the settings.
Note that when using a display that is not directly connected to the GPU being used, you will see a warning that this may result in performance being limited by the PCI Express bandwidth. Using a display that is not attached to the GPU being used for rendering requires copying the image from the GPU being used for rendering to the GPU with the display attached. This adds overhead and can cap your framerate due to bandwidth limitations. Actual results may vary depending on the resolution and exact hardware configuration.
This may also occur on systems that have multiple dedicated GPUs with monitors attached to more than one GPU. Normal two-card multi-GPU systems have monitors only attached to the primary GPU and are unaffected.