Here’s a WeakAura that adds the “Already Known” tag to Drakewatcher Manuscripts.
It’s called Dragon Customization Tooltip. We encourage you to visit wago.io and copy the import string from there to ensure your aura is up to date. In-game all Drakewatcher Manuscripts used to customize your Dragonriding Drakes, will now have the Already Known tag when already learned. Don’t forget to install WeakAuras before importing the string.
Thanks to MrGM for sharing.