I was working a defense project last year where the whole UI is a java applet that requires IE. I wonder if they're still charging ahead with the implementation.
If it’s just for Java that’s not really a problem. They might be able to run the applet directly with appletviewer, or repackage it for Java Web Start. Otherwise, CheerpJ has a solution for continuing to run the applet in the browser by converting it to WASM.
Karakun are on it though: https://openwebstart.com/