Flow version deletion constraints
Key Takeaway
To delete a flow version, first deactivate it if it is active. If it has paused interviews, wait until they finish, or delete them.
Salesforce limits when you can delete a flow version, so that you don't remove automation that is still running or waiting to resume.
Active and deactivated flow versions
A flow can have several versions, but only one is active at a time. When you activate a new version, Salesforce automatically deactivates the previously active version.