Luckily, being Linux there's a way to disable it using your favourite text editor. To disable offline updates, edit the config file /etc/xdg/discoverrc - for example using nano -
sudo nano /etc/xdg/discoverrc
Then change UseOfflineUpdates to false like so:
And then save the file and exit, which in nano is -
Ctrl+O and Ctrl X
Now when opening Discover, I can see exactly what these updates are and I shall reboot when I am good and ready!
I can kind of see some merit in trying to avoid installing some updates while the system is in use but I'd much rather just reboot or even just logout and login to KDE since sometimes that's all that's needed. i also don;t like the way it hides what those updates are, I like to see exactly what is being installed each time without resorting to using apt all the time. Making updates act like they do in Windows is a step too far!