I do not have a native package for AmigaOS 4 but a few days ago I prepared a new docker image which include gcc 11.3.0 compiled with afxgroup's new clib2 and the SDK which has most of the available clib2 libraries already installed.
I use it to compile webkit JSC and for the work we do with the port.
You can find it at
https://hub.docker.com/r/walkero/webkitondockerEven if you do not want to use it as your development environment, if you start it by sharing a folder you can grab all the required files if you share a volume between the host machine and the docker container. SDK and gcc are installed under /opt folder