Touch ID, like other features, requires that the phone be switched on or enabled before it can be utilized. Follow these steps to verify and
confirm Touch ID is active on your iPhone 8 Plus to ensure the function isn't switched off by the latest update:
- From the Home screen, choose Settings.
- Touch ID & Passcode to activate Touch ID & Passcode.
- Then double-check that the iPhone Unlock and iTunes & App Store choices are turned on.
If it's already on, turn it off for a few seconds before turning it back on. This may also assist in resolving any minor Touch ID issues that have arisen as a result of the latest iOS platform upgrades.