Unfortunately, this feature (a “Local Folders” account for messages) hasn’t been implemented yet in Mailspring. It’s been talked about for a number of years. Example:
Therefore, on Fedora Linux you’ll need to use something else for this feature, such as Claws Mail, Evolution, or Thunderbird. Claws Mail has been around for decades, is very flexible, but is fairly spartan in its user interface (which many prefer for email). Evolution is a “way of life” – it can do many things and is fairly pleasing to look at, but expects you to use it “their way” (it fully supports creating accounts with local mbox/maildir storage, though).