The upstream README says:

GTK 4 has its own scene-graph layer, GSK, which is a replacement for
Clutter.

(This does not apply to the vendored/internal fork of cogl and Clutter
in the mutter source package, which is gradually being subsumed into the
mutter codebase.)

    smcv

Clutter has now been moved to https://gitlab.gnome.org/Archive/clutter and
it's in the process of being archived. After that has happened, no new
bugs can be reported, no new commits can be pushed, and no new releases
will be made.

    smcv

We released Debian 12 and 13 with the unmaintained cogl and clutter-1.0
libraries, but I think it's time we finally remove them during the
Debian 14 cycle.

clutter-gst-3.0, clutter-gtk and libchamplain are "larger" libraries
that depend on clutter-1.0, so they will have to be removed at the same
time (or perhaps earlier, if their reverse-dependencies allow).

Similarly ibus-clutter and clutter-imcontext will need to be removed at
the same time as clutter-1.0; they would not be useful in its absence
anyway.

     smcv