Hello, I have an issue about app icons which I added to the panel. When I click and open them, they don't highlight. I want to the icons would be highlighted like Manjaro KDE edition. For example:



Any way to do this?

You can try out different desktop themes: In System Settings go to Workplace Appearance -> Desktop Theme. This shows the list of currently-installed themes as well as a button to Get New Themes which you can use to download themes from store.kde.org.
I'm pretty sure Manjaro uses a custom desktop theme, while Kubuntu primarily sticks to the defaults.

It's solved. Just added "Icons-only Task Manager" widget to the panel.