/p group GUESTS denydefault explicitly sets all default permissions for a GUESTS group. In detail, it means this: Every allowed active permission, inherited or othervise applicable, is explicitly allowed for the group. Every equally denied permission is explicitly denied. Everything else is denied. The permissions will be saved to the group config, i.e. after /feperm save or a server shutdown, and you will be able to edit them by hands. Do note that manual editing is not recommended, but sometimes necessary, when you make bulk changes. Don't forget to ensure that your backups are complete and ready to deploy.

I'm using Regrowth Modpack. After I make my groups and use /feperm save, I can not find any group config file anywhere. I have looked in world/FEData, and everywhere else. Any help would be appreciated.

As we moved to 1.12.2, is this still an issue? Closing this issue in 7 days if no response @Maxxgold