Some application icon showing as penguin alongside the original icon in Plank

How do I get just the application icon instead of penguin icon in the plank when the application is active. Not all the app icons is shown as penguin but this app “kmcaster” that I installed from flathub seems to have this issue when opened.

I tried changing the icon from alacarte and also manually but to no avail. It’s just been a month I started using Linux, so my apology if this question sound silly.

kmcaster is a java based application and the penguin icon is just the expected icon for java runtime.

It may be not handsome but it’s not really a bug nor a mistake : java is running so it shows in plank.

I don’t know if there is a way to « exclude » icons from showing in plank ?