Unfortunately, the Nintendo Switch won't turn off as easy as pressing the power button to shut it down. Pressing the power button on the tablet will put the console into a Sleep Mode instead of turning it off, you’ll need to bring up the power options menu to turn it off entirely.
Here’s how it works:
Hold down the power button on the top of the screen for around five seconds
You’ll see a menu that offers you sleep mode or power options, select power options
You can then choose to restart or turn off the system. Choose to turn it off.
You will then have fully powered down the Switch! Although it may seem simple, some may be surprised that there is no way to turn off the console via the joy-cons or any other controller used with the console.