Google Pixel 4a screen or touch input is not working correctly

The checks in more detail

Check the software. The 4a has reached the end of its updates, so keep apps up to date and clear the cache of any app that misbehaves. Boot into Safe mode by holding the power button, then touching and holding Power off and choosing OK on Reboot to Safe Mode; if touch works normally there, a downloaded app is the cause, so uninstall recent ones. In Settings, System, Gestures, check that nothing alters touch response, and turn on Show taps in Developer options to see where the phone registers touches. A dead strip or touches that appear elsewhere on the screen point to the digitiser.

Hardware aging matters at this age. A fall, even without a crack, can damage the display or its connector, and a swollen battery can push on the screen layers and cause odd touch behavior; if the display lifts at the edges, stop using the phone and see a repairer. A screen replacement fixes most hardware touch faults, though its cost may approach the phone's value. Back up with Google One before service. If the touch behavior changes with temperature, the screen may be failing. Use the Pixel's built-in diagnostics in the Pixel Tips or Device Care apps, if available, and contact a repair service with the serial number if the problem remains.

The Pixel 4a's OLED panel has a well-known behavior on this model: after years of use, a faint band of ghost touches can appear near the top of the screen when the phone is charged on a cheap cable, and the fix is a quality USB-C cable and adapter. Google's Pixel Tips app also has a touch sensitivity setting for use with screen protectors in Settings, Display, which you can try. If the touch problem appears only with a case on, the case may be pressing the edge of the screen, and a looser case solves it.