This is because the icons are pulling from the active icon theme, and the Breeze icon theme doesn't have a Krita icon in it (The Krita people requested its removal IIRC). So the generic "blank document" icon appears instead. We might have to provide a local copy of it.
Fixed with https://invent.kde.org/ngraham/welcome-app/commit/c13c9e6f9be50e4c370dfcce20997e0bd3f26bdd