Version 4.5-9 of docbook is marked for autoremoval from testing on Thu 30 Jun 2022. It depends (transitively) on nvidia-graphics-drivers-tesla-470, affected by #1011146. You should try to prevent the removal by fixing these RC bugs.
Depends on packages which need a new maintainer
normal
The packages that docbook depends on which need a new maintainer are:
This package has been
orphaned. This means that it does not have a real
maintainer at the moment. Please consider adopting this package
if you are interested in it. Please see bug number #802363 for more information.
Standards version of the package is outdated.
wishlist
The package should be updated to follow the last version of Debian Policy
(Standards-Version 4.6.1 instead of
4.6.0).