ADDITIONAL SYSTEM INFORMATION :
Fedora 34 with either OpenJDK 16.01, 16.02, or 17 EA releases - I've tried it with all three versions. I also tried it with a directly rpm-installed version of OpenJDK.

A DESCRIPTION OF THE PROBLEM :
When I try to create a ".rpm" installer using jpackage on Fedora:
     jpackage --name MyApp --app-version 1.0.0 --icon /some/path/bigLogo.png --input ./ --main-jar my_app.jar
I get an error message from jpackage:
     Error: Invalid or unsupported type: [null]
The same thing happens if I specifically request 'rpm':
     Error: Invalid or unsupported type: [rpm]

For comparison, when I install the identical JDK on an Ubuntu instance, the above command (without specifying --type rpm) works. Specifying "--type rpm" on Ubuntu also doesn't work - even though jpackage --help tells me it is a supported format.
I asked for help on stack overflow here - but no help:
https://stackoverflow.com/questions/68746207/unable-to-create-a-jpackage-installer-on-fedora-but-it-works-in-ubuntu-macos-a

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
1. Install Fedora 34 on a VM or real machine
2. Go to https://jdk.java.net/16/ and download the x64 tar file for OpenJDK 16.02
3. Extract the tar file somewhere and setup PATH and JAVA_HOME
4. Go to a directory with an application jar and its needed libraries.
5. Run jpackage similar to above

Alternatively, install JDK via "sudo dnf install java-latest-openjdk-devel" - it makes no difference in eventual result.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
I expect a ".rpm" file in the directory where I ran the jpackage command
ACTUAL -
On Fedora, I get the above mentioned error.
On Ubuntu, it works as expected. On macOS it works as expected. On Windows it works as expected.

FREQUENCY : always