I had a flow created in the default environment that needed to be moved into a solution in a managed environment. However, the export link for Package (.zip) was missing as the flow was within a default solution (preferred). It was a huge flow, and manually recreating each action would have taken a considerable amount of time. I checked another flow where the Package (.zip) was available. Upon clicking the link, I noticed that /export was appended to the URL of the flow.