This file is indexed.

/etc/xdg/knewstuff.categories is in libkf5newstuff-data 5.44.0-0ubuntu1.

This file is owned by root:root, with mode 0o644.

The actual contents of the file can be viewed below.

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org.kde.knewstuff.core knewstuff (Core Lib)
org.kde.knewstuff knewstuff (knewstuff)