What is the use case where a Data Transformation requires the creation of a Flow?
Data Transforms should take responsibility for mapping one instance of data to another.
Anyone looking to re-use that Data Transformation would not be expecting a Flow to be started.
Starting a Flow is best done from another Flow or perhaps an Activity. I would rather justify a guardrail warning on an Activity that starts a Flow than have a Data Transform start a Flow just to avoid a guardrail warning (if that's why you're doing it).