Provided that you’re going for plasma DE, you can install the Apdatifier from the KDE store.
Apart from being just a reminder, it can take care of a number of more tasks:
• Notification for updates and news
• Searching updates for Arch (+AUR), Plasma Widgets, Flatpak
• Bash script with useful options for managing packages
• Two types of lists: compact and extended with additional information
• Button to initiate a full system upgrade in the selected terminal
• Option to refresh the mirrorlist with the latest mirrors filtered by speed
• Customizable icon on the panel and package icons in the list