They don’t appear to be recorded as notifications, despite appearing as such. This makes reporting quite difficult with a short timeout.
For instance, when reporting 476306 – KWin5 crashes when Subnautica from Steam disables Fullscreen mode., I was playing a fullscreen game.
You could use for example coredumpctl Core dump - ArchWiki to view your crashes.
Also while researching I found out that KDE has a GUI for coredumpctl:
Just type drkonqi-coredump-gui into konsole to start it.
Haven’t found a way to automatically report to bug.kde.org like the DrKonqi notification does. Which is what you probably want?