I have a NVIDIA card(GTX 1080),downloaded and installed the latest driver(game ready driver:418.56),the GPU option can't be found in maya render setting,Is this version not creator ready driver?
Can you confirm the version of MtoA you have installed (Arnold > About)
Also, what do you see in the system tab of the render settings?
Can you post an Arnold log? You can just render an empty scene with verbosity level = Info
that doesn't look like the latest MtoA, in fact it looks pretty old, can you confirm what version is mentioned in the Arnold > About menu?
How are you setting the environment for MtoA, are you just setting MAYA_MODULE_PATH?
Because it looks like Maya is loading the python modules from an older mtoa.