Some of the popular causes why an Android device may freeze are temporary system slow down, Incompatible or poorly-coded app, overheating, slow performance & hardware malfunction, you can hold down the Volume Down Key and the Power Button simultaneously for 7 seconds If you have an unresponsive Samsung phone.
What can cause Galaxy to freeze or become unresponsive
the Galaxy Tab S4 has a non-removable battery, so, all you can do is to simulate the effects of having disconnected the battery by pressing and holding the Power button and the Volume button down at the same time for more than 7 seconds, This will force the device to restart it as if you’ve removed the battery and reinserted it.
You should check for a bad third party app, if your Galaxy Tab S4 works fine on safe mode (make sure that you use it for a few hours) but becomes problematic again once you return it to normal mode, that’s a clear sign of a bad app issue, Use the method of elimination to identify which one is problematic.
The S6 edge + comes with a non-removable battery, This process can be used to simulate the "battery pull" when the S6 is unresponsive, frozen, or not power on, you can ensure your device is charged to a minimum of 5%, when your battery is below 5%, the device may not power on after the reboot.
You should Press and hold the Power and Volume down buttons for 12 seconds, you use the Volume down button to scroll to the Power Down option, you can press the Home key to select, the device powers down completely, the device should be powered up in Safe Mode.