Download a specific version from the Releases page (https://github.com/graalvm/graalvm-ce-builds/releases). Note you should not take the latest by default, as Quarkus does not always support the latest version.
Unzip and move to JVM directory
sudo mv ~/Downloads/graalvm-ce-java8-20.0.0 /Library/Java/JavaVirtualMachines
/usr/libexec/java_home -V
# note the uppercase V
Sample output: