Hello,
I tried to get used to KDE activities for quite some time, but as I didn't see much benefit over virtual desktops, I recently switched back to virtual desktops to switch between work-related and other tasks. What's annoying on both, however, is their general behaviour for opening new tabs in any program (firefox, sublime, kate, basically anything that has tabs): They always open in the last-used instance, regardless of the activity/virtual desktop they are in. (My problem is the same for virtual desktops and activities, so they are replaceable in what I'm writing here and I am happy if there is a solution for either of those)

So, for example, if I recently switched back from doing some spare time stuff in sparetime-activity which included editing text-files in sublime, and then switch to the work-activity and open a text file there, it will open as a new tab in the sparetime-activity, even though there is another instance (including multiple tabs) in the work-activity as well. So I have to switch back to the sparetime-activity, move the tab out of the instance (possible in firefox and sublime, but not in many other tabbed things), change the activity this is on, and move it to the instance/window of the work-activity. This is very annoying and gets me out of my workflow often. Is there a way (either in activities or virtual-desktops) to force these programs to only consider instances/windows on the current activity/desktop?

Looking for similar issues, I found https://forum.kde.org/viewtopic.php?f=66&t=162766, but the poster of that seems to be fine with just always spawning new windows, which is not what I am looking for. I also started playing around with complex window-rules from kwin, forcing stuff to an activity by their window-name, but that gets out of hand really quickly, as I would need to make rules that categorize work/sparetime by website or something, which is unfeasible.

Running Kubuntu 22.04 with Plasma 5.24.
Thanks,
Chris