Inside flow can we use for loop , if else and other programming stuff?

Yes, but at flow level (as in within the flow, but outside of tasks) they will run at the time the flow is defined, not at the time the flow is run. If you want to control the flow of tasks run when the flow is run, see: https://docs.prefect.io/api/latest/tasks/control_flow.html

@Amanda Wee it think trigger and upstream is also useful to control task execution flow.