From here:
If your screen is black or frozen
If your screen is black or frozen, you might need to force restart your device. A force restart won’t erase the content on your device. You can force restart your device even if the screen is black or the buttons aren’t responding. Follow these steps:
– On an iPad Pro 11-inch or iPad Pro 12.9-inch: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Power button until the device restarts.
– On an iPhone 8 or later: Press and quickly release the Volume Up button. Press and quickly release the Volume Down button. Then press and hold the Side button until you see the Apple logo.
– On an iPhone 7 or iPhone 7 Plus: Press and hold both the Side and Volume Down buttons for at least 10 seconds, until you see the Apple logo.
– On an iPhone 6s and earlier, iPad, or iPod touch: Press and hold both the Home and the Top (or Side) buttons for at least 10 seconds, until you see the Apple logo.
This is on top of my Mac’s microphone not working in Skype (on MacOS, of course).
