Is this possible in dataflow?

[Imagauthamam]

Let's say we create a dataflow which contains 2 years of data. And everyday and when we refresh it it should keep the historical data (2 years) and add only today's data. The dataflow should store 2 years of data and only append today's data for every day

[SqlBobScot]

Yes, it is, and there are two options I can think of

1) if you have a Premium Capacity, you can use Incremental refresh to do what you require. Note that incremental refresh for DataFlows is unavailable for workspaces backed by a Pro licence. Incremental refresh is available for Datasets for workspaces backed by a Pro licence.

This article is a nice set of steps for setting up incremental refresh - https://debbiesmspowerbiazureblog.home.blog/2020/05/29/quick-incremental-refresh-check-list/

2) This article proposes a method for using a Data Flow in a workspace backed by a Pro licence and recreating incremental refresh - https://exceed.hr/blog/incremental-refresh-using-powerbi-pro-and-dataflows/
I've yet to try this technique.