In 18.04, whenever f.ex. Dolphin was grouped - and tooltips were disabled - clicking on the icon displayed a panel where all instances were listed vertically.
In 22.04 the behaviour is no more. Whenever I disable tooltips, nothing gets displayed.
Is it possible to get this back?
I’m guessing 18.04 refers to a Ubuntu version? But yes, it’s possible to restore this behavior. Right click the task manager (the window list) and click “Configure Task Manager…”. You’ll find an option to configure behavior when clicking a grouped task, under the “Behavior” tab. I think it’s “Shows textual list” is what you want 
Only “downside” with that is that it doesn’t have close buttons. You need to middle/ right click the task to close it.
Awesome, thank you so much!
Actually “Shows textual list” is maybe not what you want. In Kubuntu 18.04 that was a fallback, I think you want “Shows small window previews”. That’s the Kubuntu 18.04 behavior.
in Kubuntu 22.04, you’ve only got Plasma 5.24 though, which is a bit old and may not behave as well as 5.27 does here. I’d recommend upgrading to Kubuntu 23.04.