gfsview requires Mesa's libosmesa, which was removed in 2025 (Mesa
25.1.0) and is no longer available. The most recent version of Mesa that
still built libosmesa used llvm-toolchain-19, so this is one of the
factors keeping llvm-toolchain-19 in unstable.

The most recent maintainer-team upload of gfsview was in 2023, to delete
the actual gfsview GUI, which required GTK 2. There have been no updates
to the upstream source since the initial upload in 2014, and the
upstream project shows no activity since 2013. There are no
reverse-dependencies.

If gfsview is still desired in Debian, I think the only way to provide
it would be to introduce the equivalent of Ubuntu's src:mesa-compat (a
separate source package containing an outdated version of Mesa) after
which gfsview and its dependency gnome-chemistry-utils could be
re-introduced; but in the absence of anyone interested in doing that, I
think these packages should be removed.

    smcv