Gnus’ previous search engine was called nnir, and is obsolete as of
Emacs version 28. If you’ve upgraded Emacs and are now getting
obsolete-variable warnings about nnir-* variables, migration is
fairly straightforward. In addition to the variables raised by the
warnings, all previous engine-specific variables can be updated by
simply replacing the nnir- prefix with gnus-search-.
For instance, nnir-notmuch-program is now
gnus-search-notmuch-program.