Using 10W60 engine oil instead of the recommended 10W40 for your Ninja 650 2017 is not advisable. The recommended oil viscosity, 10W40, is chosen by the manufacturer based on the engine's specifications, tolerances, and operating conditions. Deviating from the recommended viscosity can potentially lead to negative effects on engine performance and longevity.
In your case, the normal summer temperature of 35°C does not warrant a significant deviation from the recommended viscosity. The 10W40 oil is designed to provide adequate lubrication and protection for your engine within that temperature range. Switching to a heavier 10W60 oil may result in poor lubrication during startup and increased internal friction, potentially leading to engine damage.
It's important to follow the manufacturer's recommendations to ensure optimal performance and reliability of your motorcycle. If you have concerns or specific requirements, it's best to consult with a qualified mechanic or the manufacturer for further guidance.