Is there a way to delete deprecated workflows?

Answer

They cannot be deleted as long as there are audit records that go along with the Cube View even if the data has been cleared. To clear this you would be required to run a reset scenario, however this clears out all workflows and data.

Typically, deprecated workflows are placed under a deprecated parent workflow and the security changed so that only admins can see these deprecated workflows.

 Source: Office Hours 2020-05-17 Partner Enablement