Scenario: Two monitors, one large one as primary and a smaller one off to the side as secondary. Thunderbird, Signal, Telegram, Discord, etc. I can’t have all of them up on a secondary monitor for reasons of a) lack of desktop space, especially when some of them only get new messages very infrequently, b) privacy - some of them have stuff that I mind people who might walk by seeing.
For the most part the notification pop up is a good compromise of ‘I can read incoming messages and the chance someone else might walk by in the 5 seconds it shows is acceptable risk’, but when I have an app fullscreen the notifications stop showing. I only have a single panel on my desktop, but some experimentation shows that even if I set up extra panels on my secondary KDE still only wants to show the notification on my primary.