Try a force restart > press and quickly release the volume up button > press and quickly release the volume down button > press and hold only the side/power button (do not slide to power off) for 15-20 seconds until the screen goes black and a white Apple logo appears and then release the side button.
Try a force restart > press and quickly release the volume up button > press and quickly release the volume down button > press and hold only the side/power button (do not slide to power off) for 15-20 seconds until the screen goes black and a white Apple logo appears and then release the side button.