Optional packages are tagged with openacs-5-2-compat.
You can check https://openacs.org/repository/5-2/ to see which packages have been tagged.
The optional packages are tagged when someone tests them and determines they meet a minimum quality level to be "released."
Personally, I have not been able to work on released many optional packages. I know that some volunteers have released packages that they use and feel are working satisfactorily on OpenACS 5.2.