In earlier releases, to add new packages to the root file system, you had to edit the <plnx-proj-root>/project-spec/meta-user/recipes-core/images/petalinux-image-full.bbappend file. For example:
IMAGE_INSTALL_append = "opencv"
From 2020.1 release onwards, you have to use the <plnx-proj-root>/project-spec/meta-user/conf/user_rootfsconfig file to append new root file system packages to PetaLinux images. For example: