When attempting to change the name of a workspace, the following error is given, despite no pending runs in the UI:
Name cannot be changed while a run has not completed
The above-mentioned validation error occurs when the workspace contains runs with a status not included in the following list:
applied, discarded, errored, canceled, policy_soft_failed, planned_and_finished, assessed, assessing
Review the Runs tab in the workspace and search for any runs which do not have those statuses, and resolve them.
It is also possible to list all runs in a workspace with the Runs API to view the current statuses across all runs: https://developer.hashicorp.com/terraform/enterprise/api-docs/run#list-runs-in-a-workspace
Once all runs are in one of the above mentioned statuses, attempt to rename the workspace again. If this is still not successful, please open a ticket with Hashicorp Support for review.