Are you sure it is related to spectacle and not to your Plasma systemsettings? Check “semi-transparency of inactive windows” or smt like that in systemsettings…
Spectacle Version 23.04.1 on Tumbleweed does not have such a problem.
Additionally some context would help: wayland or X11 session?
Any messages in a terminal?
I am not sure that this is a complete description of what you do.
When I start Spectacle (by hitting the PrintScrn key) and then choose Rectangle Region at top-right andf then click Take a new Screenshot my cursor changes into a + and I can then click a corner of what I region I want to select. The whole screen then gets a grey haze over it (but stays readable) and when I move the cursor a rectangular area without the haze is formed to denote what the rectangle is.
So there is a “fog” over the screen, but it is not unreadable.
And there is a Configure button and that shows in the General tab some option for the Rectangular Region. Did you try to play with it?
manythanks, my version is a bit different, (the version 21.12.3 on leap 15.4 on my son’e laptop is the same of your and works perfectly like your)
in my version the fog and the rectangle is like in the picture I posted, in your version is ok.
I played with configure button but without success
.config/spectaclerc >>>>has been recreated
.config/kde.org/spectacle.conf >>>this not
but the fading behaviour doesn’t change