Changelog
Updated for version 1.21.8. There shouldn't however be problems with backwards compatibility to 1.21.6.
Ancient Secrets is now a seperate datapack that is added on top of the normal Cavernous download. If you want to play with the features of Ancient Secrets then just download that file and drop it into your datapack folder.
PLEASE NOTE: if you have an older world with 2.2.2 or before on it, you will have to download both packs here. If you do want to remove the Ancient Secrets features, I plan on releasing a patch pack that will let you uninstall it in the future.