Depending on the Samsung model, the device is switched off differently; on newer models, the power button is linked to the bixby assistant, which means that the device cannot be turned off using the button.

The Samsung device can be switched off via the status bar, and the power button can also be reactivated if desired.

Android 10 (One UI 2.0)
Step 1:  Open the  notification bar
Step 2:  Tap on the  Power-Icon
Step 3:  Tap on  Power off
Step 4:  Tap again to  turn off  your phone
  1. Open the notification bar
  2. Tap on the Power-Icon
  3. Tap on Power off
  4. Tap again to turn off your phone

Samsung Instructions