On my Linux laptop with a Nvidia card, there is a Nvidia program which lets you switch between dedicated or on-board graphics, or on-demand where applications can request the graphics card. Before that the dedicated card was always on. I’m on mobile at the moment, but there is an official Nvidia website with drivers and other programs to control this. I assume the same for AMD, but I haven’t checked.
Nvidia Optimus and the selector I’m using is MATE Optimus