Hello Plxdjr1934,
Welcome to Apple Support Communities!
We want to make sure Reachability is working as expected, including in the Settings app.
Make sure the feature is enabled using these steps:
"When you use iPhone with one hand in Portrait orientation, you can use Reachability to lower the top half of the screen so it’s within easy reach of your thumb.
- Go to Settings
> Accessibility > Touch, then turn on Reachability. - To lower the top half of the screen, do one the following:
- On an iPhone with Face ID: Swipe down on the bottom edge of the screen.
- On an iPhone with a Home button: Lightly double-tap the Home button.
3. To return to the full screen, tap the upper half of the screen."
This Apple Support page has the full details: Reach the top of the iPhone screen with one hand - Apple Support
If the issue continues, try a normal restart to see if that helps to quickly resolve this.
"How to restart your iPhone 6, 7, 8, or SE (2nd or 3rd generation)
- Press and hold the side button until the power-off slider appears.
- Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
- To turn your device back on, press and hold the side button until you see the Apple logo."
Explained here: Restart your iPhone - Apple Support
We hope these steps can help isolate and resolve the issue so you can use Reachability in Settings without issue.
Cheers!