Hi @Sherazad Ahmed ,
Per my understanding, flow is more recommended.
Let me explain:
Microsoft Flow is an independent product, which can be used whether it is classic experience or modern experience. It's just that there is a link to the flow URL in modern experience which is more convenient.
If you want to use flow only in the classic experience, you can go to the flow website to create a flow, specify your list, everything is the same.
Workflow:
If you want to use workflow, you could only use SPD to create workflow 2013 now. In the past, there were some simple default workflow 2010 which can be used directly without creating in SPD, however now workflow2010 has been deprecated in SPO, so you can only use workflow2013(needs to be created in SPD,SPD is free to use).
In fact, Workflow 2013 has also come to the countdown to the life cycle as shown below:
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According to my understanding, flow is a better choice. :)
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