This image is now built and distributed as a multi-platform Docker image. This means that both a linux/amd64 and linux/arm64 version of the image are built, and Docker should automatically use the appropriate version for your computer's architecture.
By default, certification is done with 4 parallel tasks. This can be changed by overriding the ACL2_CERT_JOBS variable of the Makefile. For example, to use 2 tasks instead, run make build ACL2_CERT_JOBS=2.
To provide additional arguments to the make command that will be used to build ACL2's books, you can override the ACL2_CERTIFY_OPTS variable of the Makefile. Notice that this will override the effects of the ACL2_CERT_JOBS variable, so you will need to provide the appropriate -j option in that case.
To update the Gradescope Docker image, you first need to update the corresponding acl2-docker image. Then, update the IMAGE_VERSION value in make-gradescope.sh to match whatever was used in the acl2-docker's make-gradescope.sh script.