You should be able to move window between activities using Alt+F3 > "Show in
Activities" but with plasma 5.19 this menu is missing so you can't do that
anymore which has severe impact on activity usage
STEPS TO REPRODUCE
1. Update to plasma 5.19
Can't switch window between activities using Alt+F3 menu.
Having "Show in Activities" submenu in Alt+F3 menu.
Operating System: Arch Linux
KDE Plasma Version: 5.19.0
KDE Frameworks Version: 5.70.0
Qt Version: 5.15.0
Kernel Version: 5.4.45-1-lts
OS Type: 64-bit