I have two virtual desktops and since version 5.25 all applications are opened on the left one after boot. Previous behaviour was different and allowed to bind applications to a specific virtual desktop so it was respected on boot or when closing/opening the application. I never had to create a window rule for that, it just was the way it worked.
STEPS TO REPRODUCE
1. Open application on one virtual desktop and then close it
2. Switch to another virtual desktop
3. Reopen application
Window appears on current virtual desktop.
As opposed to before, where it will open on the last one used. And more important, that was respected also after boot.
KDE Plasma Version: 5.25
KDE Frameworks Version: 5.95
Qt Version: 5.15.4
*** This bug has been marked as a duplicate of bug 442380 ***