On page 121 of the 16.1 user manual, it describes the GPU Configuration section of the Preferences panel. For the switch "Use Display GPU for Compute", it states
..., if two GPUs are installed for image processing, this checkbox enables the shared use of the display GPU instead of dedicating it to just the DaVinci user interface.
Under what circumstances would someone want to uncheck this box? If the OP does Fusion work which I understand uses only one GPU, should he uncheck this box to make sure the Fusion processing is not slowed down by choosing to use the GPU that's driving the display?
To the OP: since it you have multiple GPUs, you can play with the GPU Configuration settings to see what effect they have on performance. (Also, if you'd put your system configuration in your signature, people might realize that you already have multiple GPUs.)