As title says, all I get is spectacle: error while loading shared libraries: libopencv_imgproc.so.413: cannot open shared object file: No such file or directory, if I downgrade opencv to 4.13 I instead get spectacle: error while loading shared libraries: libopencv_imgproc.so.500: cannot open shared object file: No such file or directory. Even downgrading spectacle itself doesn’t seem to fix the problem 
Not sure where the issue arise but if you update your system and build the package locally it will be linked against your current opencv version for sure
You can get the pkgbuild by using git clone or by using an AUR helper with the -G option
https://gitlab.archlinux.org/archlinux/packaging/packages/spectacle
cd spectacle
makepkg -sir
Thx for the report. Spectacle needs a rebuild against opencv 5.0