Arrow on every screen

Try a forced restart.

• Press and quickly release the volume up button

• Press and quickly release the volume down button

• Press and hold the side button.

• When the Apple logo appears, release the button.

https://support.apple.com/en-in/guide/iphone/iph8903c3ee6/ios

You have set some Accessibility feature.

My guess is it’s associated with Settings > Accessibility > Touch > Assistive Touch.