Clickbaity title on the original article, but I think this is the most important point to consider from it:
After getting to 1% in approximately 2011, it took about a decade to double that to 2%. The jump from 2% to 3% took just over two years, and 3% to 4% took less than a year.
Get the picture? The Linux desktop is growing, and it’s growing fast.
KDE has its own Discover thing for downloading Flatpaks FWIW.
You still need the underlying package manager installed (it’ll prompt you to do so), and on Plasma 5.0 you also need a special integration plugin for each package manager (merged into Discover since I think Plasma 6.0).
Discover is a joy to use.