I'm creating a small modpack in 1.12.2 for me and a friend and everything goes perfectly but when I hold an ancient tome the enchantment disappear and the tome became useless. In the creative inventory and in singolplayer worlds everything works well.

Hello! Quark's moved to 1.18 now-- unfortunately, this means that (unless your bug is critical and/or game-breaking), we're closing support for issues filed for versions prior to it (e.g. Quark on 1.16).

If your issue still occurs on 1.18, or if your issue happens to be rather critical (e.g. consistently crashing the game with no other mods present), please leave another note or open a new issue. Thanks for your cooperation!