Hello Suriya,
Welcome to Microsoft Community.
The Surface Go 2 obviously comes with a tablet mode, but I'm guessing you're referring here to the tablet mode in Windows 10, not Windows 11.
In Windows 10, Tablet mode is a separate feature and can be turned on at the customer's discretion. So you can turn on tablet mode even if you're connected to the Type Cover.
However, in Windows 11, tablet mode was integrated into the system, and it became an automated feature. If your Surface Go 2 is not connected to any physical keyboard, it is in tablet mode at this point. Connect the dedicated Type Cover and it will go directly into desktop mode.
Compared to Windows 10, it is a pity that in Windows 11, you cannot enter tablet mode while connecting to a physical keyboard.
Best Regards,
Mitchell | Microsoft Community Support Specialist