Best answer by Ssherjj
I'm sorry to hear you are having trouble with your iPhone. I believe that once your iPhone is updated from Apple you can not revert. You'll have to wait for another Apple update or try these steps below.
Force reboot/restart an iPhone X,XS,XS Max,XR,iPad Pro,iPod touch to fix frozen/black screen or the buttons aren't responding requires a three button procedure and it won't erase any content on your device.
iPad Pro or iPhone 8 or later:
1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Then Press and hold the side button until the screen turns off and then turns back on. You can release the side button when the Apple logo appears.
If you need more help then I'd advise that you Contact Apple Support. https://support.apple.com/contact
Hope this helps?