Dark enchanter cost a lot of xp after the newest update, making it almost useless

Already solved for next release, and already fixed in the official servers.
You can edit the config yourself for your local server/singleplayer world, or simply deleting the file will revert it back to the mods original default values.

minecraft\config\dark-enchanting.json5

Or you can grab the updated config file for the modpack from the dev branch: https://github.com/TeamAOF/All-of-Fabric-5/blob/dev/config/dark-enchanting.json5