GPG: no default secret key gpg

In Fedora, you may have both gpg and gpg2. The secret keys are stored in different ways.

Try

which gpg gpg2

You might get:

/usr/bin/gpg
/usr/bin/gpg2

If you do have both, run:

gpg2 --list-secret
gpg --list-secret

Suppose your gpg2 --list-secret returns nothing. You can then export from gpg then import to gpg2 like so:

gpg --export-secret-keys -a > secret.asc
gpg2 --import secret.asc

Note that pass phrase is required to export.
Finally, verify the import with

gpg2 --list-secret

You may encounter the error message: Unknown IPC command. The quick fix is set the environment variable LC_ALL=C