How to stop validation?

Hi margaretaak ,

Thank you for reaching out to Microsoft Fabric.
You cannot manually stop validation in Dataflow Gen2 once it starts. After clicking Publish, Fabric runs background validation with no cancel button. The only options are to check the Monitoring hub for a possible cancel action, wait for validation to finish or time out, or refresh the workspace. To prevent long validations, ensure query folding works, simplify queries, and monitor the workspace activity.
Incase if it is running for hours please do reach out to the support team for further help so they can investigate your scenario: https://support.fabric.microsoft.com/support

Hope this helps,
Chaithra E.