Per MS Support Case 118091118980919, the subject line would need added to Flow since it is not currently enabled.
I have discussed this with my Product team and found that Sharepoint has given the text display option for the “hyperlinks columns” in the list so that users can use this easily but in the flow this feature does not designed. Flow only takes the hyperlink from the SharePoint. This is by design.
If you want this feature on the flow you can post your idea in the ideas forum.