Ubuntu 23.04. It worked on it's first boot, but suddenly broke that day.
Is it possible that ksplashqml was really present, and actually the "not found" error was because ksplashqml could not find a custom splash theme file? Had you installed and removed any custom themes?
Sorry, just wanted to test-drive KDE without wiping my entire system. My friend even had this problem on KDE Neon.