Hello @luc2 and welcome to the forum!
The brushes work in Krita 5.2.2, and they also work in my 5.3.0 Nightly. But watercolor brushes are not easy to handle, in most cases you should not apply much pressure, but treat them as if you wanted to caress your canvas.
You can see the expected stroke image in the brush editor, accessible via F5 or the toolbar, in the “Display” at the top left of the brush name. There you can also immediately see every change to the settings, in real time, if you want to call it that. The thumbnail does not always have to correspond to the real line image, it is often only an approximation, and often “only” a small work of art with only a rough reference to reality.
Michelist
Add/Edit: I’m happy you have found a solution.