"Data flows" in Azure Synapse Analytics are transformations done with Azure Data Factory (well, the version of ADF embedded in Synapse):
https://docs.microsoft.com/en-us/azure/synapse-analytics/concepts-data-flow-overview
Dataflows in the Power BI service is Power Query Online. They're superficially dealing about the same type of needs, but Power BI dataflows are geared towards business users, don't scale particularly well, and offer little to no orchestration capabilities beyond a few options via the API and Power Automate. Meanwhile Azure Data Factory is a full-fledged orchestration offering, i.e. it's meant to handle entire data pipelines as well as let you choose sink/destination (for now Power BI dataflows only save data to Azure Data Lake Storage Gen 2).
