The Age of Empires: Definitive Edition Clan management via ageofempires.com has been deprecated in favor of the more feature-rich Xbox App, available on desktop and mobile.
Age DE Clans have always been backed by the Xbox Clubs service, so your existing Clan information is already there waiting for you. Using Xbox Clubs directly adds great features like Chat and LFG while still allowing you to manage your roster and other Clan information.
To get started with Clubs, install the Xbox app, and find your clan in the club section to chat, post and more!
Please note that this does not affect Age of Empires II or III.