Okay; a restart has Krita showing up now. All good. This must be one of the rare programs that Linux needs a restart for unlike Windows which needs to be restarted for every little thing. When I was a Windows tech I felt like half my life was waiting on Windows to reboot.
I have ran into that a few times. A restart will make the item show up in the menu. I think they are there and can be run from the terminal but just not in the menu yet? Now there is something that would be handy and missing from Linux, an alert notice that it might need to be restarted for the item to show up in the menu. Like you, I had to figure that one out on my own.
It's *possible* that merely logging out and back in would have fixed it.