I use Kubuntu 24.04. The other day I received a low disk space notification. Later, I could not find it – or any notification history - despite references in Settings and elsewhere to history. Where the heck is it?
do you have notifications icon in the system tray?
if you enable that and open it there should be history there you can browse.
if not you can use journalctl or ksystemlog to browse the logs and look for your error message by date and key words.
Strangely, if you deliberately remove a widget, you get a persistent pop-up that won’t go away… but generally it’s up to the application to manage.
I like the feature I have on Android, with ‘Notistar’ which keeps a persistent backup of all notifications that have passed the lock screen (i.e. if I read them, or swipe them from the screen I can call them up again in Notistar).
It might be a good idea for a request for this - a persistent backup for notifications, perhaps with the ability to log them all with some advanced settings (e.g. Log All for 1 hours, Log critical for 1 week).