Microsoft 365 Copilot is only supported on primary mailboxes that are hosted on Exchange Online. It is not available on a user's archive mailbox, group mailboxes, or shared and delegate mailboxes that they have access to.
There is no specific timeline mentioned for when Copilot will be available for shared mailboxes. However, you can stay updated by subscribing to the RSS feed for any future announcements regarding this feature.
Thanks,
Prasad Das
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