How to turn off news popup in KDE tray
These are probably notifications sent by your browser generated if you give a web site permission to send you desktop notifications. Here's an example:
For Chromium and Google Chrome, type chrome://settings/content/notifications in the address bar and press Enter. Then, enable/disable notifications as desired remembering to activate "Ask before sending".
For Firefox, type about:preferences#searchResults in the address bar and press Enter. Click on Select next to notifications and make your choices.
Other browsers may have similar settings.