Settings are unavailable and inactive

It is hard to visualize what you are seeing or if it is a message that pops up. It may be helpful to provide a screenshot.

In the meantime, perform a Force Boot on your phone that will resolve many problems due to cache issues.

• Press and quickly release Volume up
• Press and quickly release Volume down
• Press and HOLD side button until the Apple logo appears. This may take up to 15 seconds while holding the side button until you see the Apple logo. Ignore anything else you see on the screen, including the slide to power off prompt, until you see the Apple logo. If the Apple logo does not appear within the 15 seconds, try again as it may take a couple of attempts to get the speed and sequence of the key presses correct.

Do you have a VPN installed? If so remove it, just turning it off may not resolve the problem.

What do you have listed at Settings > General > VPN & Device Management?