This builds on bug 919218, "non-transition: libqt5gui5-gles",
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=919218

There are still ~23 packages that are broken (forcibly uninstalled)
in response to installing libqt5gui5-gles, 7 by omitting the OpenGL
alternative and 16 by a dependency-listing bug.

As an alternative to fixing all of these packages, you could rename
the current libqt5gui5 package as something like `libqt5gui5-nogles`
and then create a new `libqt5gui5` package that simply depends on
`libqt5gui5-nogles | libqt5gui5-gles`.


The rest of this post is about identifying those 7+16 broken packages.

An initial query shows 8 (-1 since qtbase5-dev has qtbase5-gles-dev):

$ grep-dctrl -n -sPackage -FDepends -e 'libqt5gui5[[:space:]]' --and
--not 'libqt5gui5-gles' 
/var/lib/apt/lists/deb.debian.org_debian_dists_unstable_*_binary-*Packages

elektra-qt-gui
mldemos
openscad
python3-pyqt5.qtopengl
python3-pyside2.qtopenglfunctions
libqt53drender5
qtbase5-dev
libqt5datavisualization5

However, there are some problems in other packages, like
audacious-plugins, which accidentally lists libqt5gui5 twice
(just like Dmitry's mention of libqt5quick5 on 2019-12-09):

libqt5gui5 (>= 5.1.0), libqt5gui5 (>= 5.14.1) | libqt5gui5-gles (>=
5.14.1)

so a better search would simply be to search for a dependency on
libqt5gui5 that lacks alternatives:

$ grep-dctrl -n -sPackage -FDepends -e 'libqt5gui5[[:space:]][^|]+,'
/var/lib/apt/lists/deb.debian.org_debian_dists_unstable_*_binary-*Packages

audacious-plugins
cloudcompare
colmap
doomsday-common
elektra-qt-gui
gammaray-plugin-quickinspector
krita
mixxx
mldemos
nextpnr-ice40-qt
libopenms2.6.0
openscad
python3-pyqt5
python3-pyqt5.qtopengl
python3-pyside2.qtgui
python3-pyside2.qtopenglfunctions
libqt53drender5
libqt5opengl5
qtbase5-dev
libqt5datavisualization5
libqt5quick5
shotcut
libsight
stellarium

That's the full list, including the 16 with erroneous dependencies,
just like audacious-plugins. We can confirm that with:

$ grep-dctrl -n -sPackage,Depends -FDepends -e
'libqt5gui5[[:space:]][^|]+,'
/var/lib/apt/lists/deb.debian.org_debian_dists_unstable_*_binary-*Packages
|grep -E -B1
'[[:space:]]libqt5gui5[[:space:]][^,]*,[[:space:]]libqt5gui5[[:space:]]'
|awk 'NF==1 && $1!="--"'

(I don't know how to better search with grep-dctrl, so I had to filter
through grep. The awk command simply extracts the package names from
grep's filtered output.)