On my '18 Buick Tour-X there is no option to disable. I paid $500 for a Trifecta tune which disables the feature and also boosts power, changes shift points, etc.
The factory programming for auto-start/stop is terrible when it comes to timing/prediction. It will shut off at the slightest stop. The implementation of it is fine, very seamless. Fortunately the Trifecta tune allows you to revert to stock settings by arming the cruise control. Start/stop is there when I want it and there's plenty of times that I do.
The only workaround prior to the tune was to put the car in neutral or manual-shift mode, but I felt like I was going to wear out the shifter as much as I used that method.