Touching the end call button is all it takes to hang up and disconnect an ongoing (incoming or outgoing) call. But if you want to end calls with power button on HTC 10, you first need to do as follows and after that the call will be ended as soon as your press this physical buttons:
1. Drag down the notification bar and touch the Gear icon to open the Settings app
2. Scroll down to the Personal settings, and touch to open the Accessibility settings
3. Now, scroll down again to the System settings and simply toggle ON the Power Button Ends Call button
4. You are all setup and from now on, you don't have to touch the screen to end a call on HTC 10.