Hello,
since the update to Plasma6, the Spectacle window is no longer hidden during a recording. This means that the Spectacle window is always visible during a full-screen recording. When recording a rectangle, Spectacle must always be moved out of the area to be recorded.
I’m still on X11 and using an AMD graphics card with amdgpu driver.
I tried to uninstall Spectacle, renamed the config file ($HOME/.config/spectaclerc) and installed spectacle again, but this didn’t help.
The problem doesn’t occur for another user who never used Spectacle before.
This is an example of a rectangular screenshot while Spectacle is still visible on the screen.