Read the owners manual. Dexos is a easy spec to make, all synthetic oils will pass that, at least name brand ones.
Many, maybe all, name brand 'blends' will pass that spec as well.
The new DI engines are hard on oil. Fuel dilution is back.
Hence the spec for better oil.
My manual says something to the effect that IF Dexos oil is not readily available, a good quality conventional 5W-30 can be used.
I use synthetic in everything from the lawn mower up, so I ignore what GM says in reference to oil.