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

Calculating dependencies ... done!
Dependency resolution took 0.99 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "sci-libs/hdf5:=[mpi=]" has unmet requirements.
- sci-libs/hdf5-2.2.0::gentoo USE="hl threads zlib -cxx -debug -fortran -mpi -szip -test -unsupported"

  The following REQUIRED_USE flag constraints are unsatisfied:
    !unsupported? ( threads? ( !hl ) )

  The above constraints are a subset of the following complete expression:
    !unsupported? ( at-most-one-of ( cxx mpi ) threads? ( !cxx !mpi !fortran !hl ) )

(dependency required by "sci-libs/vtk-9.6.2::gentoo" [ebuild])
(dependency required by "=sci-libs/vtk-9.6.2" [argument])