Hello OP, on this kind of system GNOME should use the igpu by default and the dGPU only when an App “launched with dedicated graphics” from the menu, or with DRI_PRIME=1 from the command line. (Also some vulkan game can also select the dgpu)
If that is not the case this is a bug.
Are you using x11 or wayland, can you see what is using the dgpu with nvtop ?