Nvidia discontinued the development of the CUDA Toolkit for macOS. The last version that was release for it was 10.2. Consequentially, Blender 2.9x does not include support for CUDA rendering on macOS. This change is documented in the release notes and the manual.
NVIDIA GPU rendering on macOS is no longer supported. Apple dropped support for CUDA drivers ...
You are enabling Open Shading Language.
Currently it's only support by CPU instruction.
Disable it first.
Please check your preference setting,
Check only GTX 1080 for CUDA device, save the preference and you might need to restart your Blender (most of the time don't need).