Half of my iPad M4 screen is flickering green

As described, your iPad has a hardware fault that requires repair. You would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) where the technicians will be able to test and assessed your iPad - and you can explore your available options for repair:

Genius Bar Reservation and Apple Support Options - Apple

Alternatively, you might entertain sending your iPad for repair:

iPad Repair and Service - Apple Support

For practical purposes, in lieu of repairing and returning your own iPad, Apple usually exchange the iPad for a renewed/refurbished iPad of the same model and specification.

if it was me then I would try

Force restart iPad - Apple Support

if it kept doing it then I would

Reset iPad settings to their defaults - Apple Support

if it kept doing it then I would assume it would require repair