What’s happening?
When attempting to assign published knowledge articles to a user or team in Dynamics 365, an error occurs preventing the assignment.
Reason:
This behavior is by design. Dynamics 365 does not allow published knowledge articles to be directly assigned to users or teams.
Resolution:
To assign a knowledge article to a user or team, a published article must first be changed to a different state, such as "Draft". This can be done by selecting the Revert to Draft button from the command bar. After changing the state, the article can then be assigned to the desired user or team. Once assigned, the knowledge article can be published again.
More information: Review knowledge articles | Microsoft Learn