try and launch it from terminal passing the full url https://<local ip here> :8443/admin.jnlp as a parameter since it's giving you the java 2 + notice.
https://codingtechroom.com/question/-run-jnlp-files-terminal-mac
You can also try and use a VM or other Windows emulator and use Microsoft Edge in "IE compatibility mode".
https://javatechniques.com/blog/launching-java-webstart-from-the-command-line/
I do know they're trying to kill java any way they can and that means most modern browsers can't run the java apps which is why the UDI ui is switching to a browser based solution for managing things. I use icedtea-web to make it work on my systems which is also another solution if you're ok with installing a dedicated app.
