To Disable a flow step, click the gear icon of the step you want disabled and select the appropriate option:
If any downstream steps have Step Criteria (Filters, Enhancements, or Deliveries) related to this step, a Warning prompt will appear. As the warning says, flow behavior will be unpredictable, especially if these downstream steps rely on appended data from the Disable Step.
After disabling a step, that step will be marked, along with any subsequent affected steps:
To Enable a step, use the same menu and choose the appropriate option: