keyboard and trackpad unresponsive on MacBook Air 2020

Use an external keyboard & mouse.

More than likely you have a hardware issue with this laptop. Have Apple or an Apple Authorized Service Provider examine the laptop to confirm & provide you with a repair estimate. If it is an Intel Mac, then I personally would not spend any money on it for multiple reasons. The money spent on repairs is better put towards a new laptop. The M-series Macs will run circles around an Intel MBAir.

If it is an M-series Mac, then the issue could be as simple as a bad Lid Angle Sensor....yes, for some reason it can affect the Keyboard & Trackpad according to my co-worker. Otherwise the issue could be with the Keyboard, Trackpad, or Logic Board. With Macs, an issue with either the Keyboard or Trackpad can result in both of them not working.

A swelling failed battery can cause unexpected input behavior from the keyboard and trackpad. Have you checked for that? Things you can check at home:

•The gap between the display and the deck is not even when the display is closed.

•The gap between the bottom plate and chassis is uneven in places.

•Some of the screws that hold the bottom plate have popped out.

•The trackpad surface is higher than the surrounding deck surface.

•The computer "rocks" a bit on a known flat surface†.

† —I find solid-surface and granite countertops very effective flat test surfaces.

Try booting into Safe Mode to see if it makes any difference.

Also try booting the Apple Diagnostics to see if any hardware issues are detected or if it will even load & run the diagnostics.

Do you have access to another working Mac that can run macOS 15.x Sequoia?