On Wayland, when I use a keyboard shortcut to move a window to a different workspace / virtual desktop on a system with two monitors, the window flickers a lot, but stays visible on the current workspace. Clicking it makes it disappear, though while it is still visible you can use a keyboard shortcut again to move it to yet another workspace (or back to the current one).
This issue does NOT occur with just one monitor (but I think it used to). It also does NOT occur if instead of a keyboard shortcut, the Alt+F3 menu is used to move the window to a different workspace
STEPS TO REPRODUCE
1. Be on Wayland and have more than one monitor
2. Have >1 workspace and set KWin keyboard shortcuts for moving a window to a specific workspace
3. Use the shortcut to move a window to a different workspace
The window flickers and stays visible on the current workspace even though it was moved to a different one
The window should simply disappear since it is no longer supposed to be on that workspace.
Operating System: Arch Linux
KDE Plasma Version: 5.23.3
KDE Frameworks Version: 5.87.0
Qt Version: 5.15.2
Kernel Version: 5.14.16-zen1-1-zen (64-bit)
Graphics Platform: Wayland
... and also on KDE Neon unstable
Your description looks very similar to mine issue with moving windows with shortcuts to other activities and virtual desktops. https://bugs.kde.org/show_bug.cgi?id=444172.
Indeed, that seems to be the same issue.
*** This bug has been marked as a duplicate of bug 444172 ***