It seems that it is not your table structure.

There are three possible blockers, check them in this order.

Dataverse search is not enabled : this is the most likely one. It is an admin setting that is off by default in many environments. Your Power Platform admin needs to turn it on at admin.powerplatform.microsoft.com, and make sure the relevant columns on your table are marked as searchable.

Doc: https://learn.microsoft.com/power-platform/admin/configure-relevance-search-organization 

Your agent authentication is wrong. Dataverse knowledge sources require the agent to be set to "Authenticate with Microsoft". Go to Settings > Security > Authentication in Copilot Studio and confirm that is what you have.

A DLP policy is blocking it. If your organisation has Data Loss Prevention policies restricting Dataverse connectors, the knowledge source will silently show as Unknown. Your admin can check this in the Power Platform admin center.