With current browsers Java applets are not supported anymore. Some older HPE systems the didn't update the firmware to provide alternatives.

I've seen multiple vendors with problematic code that didn't work with newer Java versions.

This is by no means meant to bash Java. Some non-Java BMCs can be horrible as well (e.g. require many TCP ports in a firewall/tunnel unfriendly way or require SSH with old algorithms that are no longer enabled by default, or telnet..)