ADDITIONAL SYSTEM INFORMATION :
macOS Catalina 10.15.6
Java(TM) SE Runtime Environment (build 1.8.0_261-b12)

A DESCRIPTION OF THE PROBLEM :
It is a regression of Bug ID JDK-8160500. I searched in jreinstall.log and executed the installer from Terminal, and no error was printed. But when I try to launch a Web Start application using jnlp or jnlps protocol, Safari can't handle it.

To resolve the issue I and then I was able to launch the application.

REGRESSION : Last worked in version 8

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
With a fresh macOS system, download and install the latest JRE installer and try to execute an application using the protocols jnlp or jnlps.

If you uninstall the JRE and tries to replicate this bug it won't be reproducible because the uninstaller doesn't clean the protocol handlers itself. You need to clean it before uninstall with:

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -R -u -f "/Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Resources/JavawsLauncher.app"

Or if you already uninstalled run with -kill parameter to rebuild the database.

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Browser opening a popup asking for permission to launch “JavawsLauncher”.
ACTUAL -
Safari or any other browser can't handle the protocols.

---------- BEGIN SOURCE ----------
jnlps://docs.oracle.com/javase/tutorialJWS/samples/deployment/dynamictree_webstartJWSProject/dynamictree_webstart.jnlp
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
Manually execute JavawsLauncher.app (/Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin/Contents/Resources).

FREQUENCY : always