Have just done a fresh installation from the online installer, chosen KDE plasma and Cinnamon. Booted into plasma, and there is an icon 3rd from left at bottom, for Discover. However it doesn’t do anything, as Discover has not installed. It did do so automatically on another installation from the previous ISO.
We do not support using Discover for package-management and it was confusing users, but plasma changed to have the starter on panel per default, so because we do not have a theming setup (and will not do) for plasma the default configuration show that icon, simple releasing it will solve it.
Thought as much, thanks @joekamprad.