It is generally recommended to follow the manufacturer's guidelines and recommendations for oil grade during the break-in period of a motorcycle. In your case, the owner's manual for the Suzuki Gixxer SF FI suggests using a 10W40 oil grade.
During the break-in period, the engine components are still settling in and achieving optimal fitment. Using the recommended oil grade ensures proper lubrication and helps facilitate the break-in process.
While the Motul 3000 4T Plus 20W40 is a high-quality oil, it has a different viscosity (thickness) compared to the recommended 10W40 oil grade. Using a higher viscosity oil may affect the engine's performance during the break-in period and could potentially impact the warranty coverage.
To ensure the best performance and longevity of your motorcycle, it is advisable to stick with the recommended 10W40 oil grade during the break-in period as specified in the owner's manual. Once the break-in period is complete, you can consider discussing oil options with a trusted mechanic or the manufacturer's authorized service center for any potential recommendations or changes based on your specific riding conditions and preferences.