Back when I was still on macOS, that was pretty standard: most Java processes showed in the Dock like that. I can't remember the exact conditions on when it does or does not show up -- but it's "normal".

Thanks. I've never seen it before but good to know its just a thing that happens...

I do not get that in my Dock

This issue seems similar to what you have: https://discussions.apple.com/thread/250160716