I have the same problem since the Update of my Thinkpad (embedded graphics) from 22.04 to 24.04.
I found that solved Plasma6 topic from April, but that did not help me.
Compositor is turned on - turning on and off did not change the behavoiur of Spectacle.
Any other idea what might help to blend out the spectacle window during screenshots?
Thanks.
Ok, solved.
Deleted the old spectaclerc in $HOME/.config and it works again.