I have a flow in which there are two dropdown fields. By default Salesforce makes these fields mandatory (No complaints) but it is defaulting the first choice value. I want that not to happen. I want the flow to provide a default option like "--Select One--". In reality, I can create a separate option called "--Select One--" but then to enforce the validation I will need to add couple more screens and assignments to validate the inputs. It will not be scalable if in the future I add more and more dropdown fields.
I know from working with VF and other sources that if there is no "none" option that usually means that the field is marked as required in the field definition. This is evidenced by the fact that they are marked as mandatory in your flow.
You can remove the required flag on the field and update all the page layouts to show that field as required. This will make sure end users have to enter a value but allows you more flexibility in your automations.
I believe it's also possible to add a "none" option to the picklist in the record type definition if you are using record types for your object. From my experience this is only enforced if the record already has a record type (if you're editing an existing record or if you create a new record and explicitly set the record type before showing the fields to your user). This is something I've done in Visualforce, I'm not sure how well it'd work in a flow but it could be worth a try.