Gentoo ~ # emerge --update --deep --newuse @world -a

These are the packages that would be merged, in order:

Calculating dependencies... done!

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

media-libs/opencv:0

  (media-libs/opencv-4.1.2-r3:0/4.1.2::gentoo, ebuild scheduled for merge) USE="eigen features2d ffmpeg gstreamer jpeg jpeg2k opencl opengl openmp png python qt5 threads tiff vaapi (-contrib) (-contribcvv) (-contribdnn) (-contribhdf) (-contribsfm) (-contribxfeatures2d) (-cuda) -debug -dnnsamples -download -examples -gdal (-gflags) (-glog) -gphoto2 -gtk3 -ieee1394 -java -lapack -opencvapps -openexr (-pch) (-tesseract) -testprograms -v4l (-vtk) -webp -xine" ABI_X86="(64) -32 (-x32)" CPU_FLAGS_X86="avx avx2 fma3 popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3" PYTHON_TARGETS="python3_7 -python3_6" pulled in by
    (no parents that aren't satisfied by other packages in this slot)

  (media-libs/opencv-3.4.1-r7:0/3.4.1::gentoo, installed) USE="eigen ffmpeg gstreamer gtk jpeg opencl opengl openmp png python qt5 threads tiff vaapi (-contrib) (-contribcvv) (-contribdnn) (-contribhdf) (-contribsfm) (-contribxfeatures2d) (-cuda) -debug -dnnsamples -examples -gdal (-gflags) (-glog) -gphoto2 -ieee1394 -java -lapack -openexr (-pch) (-tesseract) -testprograms -v4l (-vtk) -webp -xine" ABI_X86="(64) -32 (-x32)" CPU_FLAGS_X86="avx avx2 fma3 popcnt sse sse2 sse3 sse4_1 sse4_2 ssse3" PYTHON_TARGETS="python3_7 -python3_6" pulled in by
    >=media-libs/opencv-2.3.0:0/3.4.1= required by (media-plugins/frei0r-plugins-1.6.1:0/0::gentoo, installed) USE="facedetect scale0tilt -doc" ABI_X86="(64)"
                             ^^^^^^^^^                                                                                                                          

dev-python/pygments:0

  (dev-python/pygments-2.6.1:0/0::gentoo, installed) USE="-doc -test" ABI_X86="(64)" PYTHON_TARGETS="python3_7 (-pypy3) -python3_6 -python3_8 (-python3_9)" pulled in by
    (no parents that aren't satisfied by other packages in this slot)

  (dev-python/pygments-2.5.2:0/0::gentoo, ebuild scheduled for merge) USE="-doc -test" ABI_X86="(64)" PYTHON_TARGETS="python2_7 python3_7 (-pypy3) -python3_6 -python3_8 (-python3_9)" pulled in by
    dev-python/pygments[python_targets_pypy3(-)?,python_targets_python2_7(-)?,python_targets_python3_6(-)?,python_targets_python3_7(-)?,python_targets_python3_8(-)?,python_targets_python3_9(-)?,-python_single_target_pypy3(-),-python_single_target_python2_7(-),-python_single_target_python3_6(-),-python_single_target_python3_7(-),-python_single_target_python3_8(-),-python_single_target_python3_9(-)] required by (dev-python/docutils-0.16:0/0::gentoo, installed) USE="" ABI_X86="(64)" PYTHON_TARGETS="python2_7 python3_7 (-pypy3) -python3_6 -python3_8 (-python3_9)"
                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                


It may be possible to solve this problem by using package.mask to
prevent one of those packages from being selected. However, it is also
possible that conflicting dependencies exist such that they are
impossible to satisfy simultaneously.  If such a conflict exists in
the dependencies of two different packages, then those packages can
not be installed simultaneously.

For more information, see MASKED PACKAGES section in the emerge man
page or refer to the Gentoo Handbook.


!!! The ebuild selected to satisfy "media-gfx/imagemagick" has unmet requirements.
- media-gfx/imagemagick-7.0.10.23::gentoo USE="X bzip2 cxx fpx graphviz hdri jbig jpeg jpeg2k openmp pango png raw svg tiff webp wmf zlib -corefonts -djvu -fftw -fontconfig -heif -lcms -lqr -lzma (-opencl) -openexr -perl -postscript -q32 -q8 -static-libs -test -truetype -xml" ABI_X86="(64)"

  The following REQUIRED_USE flag constraints are unsatisfied:
    svg? ( xml )

  The above constraints are a subset of the following complete expression:
    corefonts? ( truetype ) svg? ( xml ) test? ( corefonts )

(dependency required by "app-misc/neofetch-6.0.0::gentoo[X]" [installed])
(dependency required by "@selected" [set])
(dependency required by "@world" [argument])