Second RESTRICT was cancelling out the first one.
Package-Manager: Portage-2.3.42, Repoman-2.3.9
DESCRIPTION="Powerful scientific data visualization application"
HOMEPAGE="https://www.paraview.org"
SRC_URI="https://www.paraview.org/files/v${MAJOR_PV}/${MY_P}.tar.gz"
-RESTRICT="mirror"
LICENSE="paraview GPL-2"
KEYWORDS="~amd64 ~x86"
SLOT="0"
IUSE="boost cg coprocessing development doc examples ffmpeg mpi mysql nvcontrol openmp plugins python +qt5 sqlite tcl test tk"
-RESTRICT="test"
+
+RESTRICT="mirror test"
REQUIRED_USE="python? ( mpi ${PYTHON_REQUIRED_USE} )
mysql? ( sqlite )" # "vtksqlite, needed by vtkIOSQL" and "vtkIOSQL, needed by vtkIOMySQL"