Hi,
So it took me a while to figure out how to make it work so i tought i share what i found with the community.
Java is no longer supported in firefox and chrominium for a while now. The litterature you find on the internet is to install IcedTea on linux but all the repo are now empty since it's no longer supported.
What you need to do is to download it via terminal with this command
sudo apt install icedtea-netx
Then, download the admin consoli by entering your ISY994 ip adresse. After this step go to the downloaded file folder and run
javaws admin.jnlp
You now have the admin consol running on the latest linux.
For me, i am running on LUBUNTU in october 2020